(1999). "Novel approach implemented to cavity ring-down spectroscopy." Journal Of Research Of The National Institute Of Standards And Technology 104(4): 418-419.

(2003). "Cavity ring down spectroscopy analyses flames." Trac-Trends In Analytical Chemistry 22(1): III-IV.

Aarts, I. M. P., B. Hoex, et al. (2004). "Direct and highly sensitive measurement of defect-related absorption in amorphous silicon thin films by cavity ringdown spectroscopy." Applied Physics Letters 84(16): 3079-3081.

Cavity ringdown spectroscopy has been applied to hydrogenated amorphous silicon (a-Si:H) showing that this fully optical method is suited for the detection of defect-related absorption in thin films with a minimal detectable absorption of 1x10(-6) per laser pulse and without the need for a calibration procedure. Absolute absorption coefficient spectra for photon energies between 0.7 and 1.7 eV have been obtained for thin a-Si:H films (4-98 nm) revealing a different spectral dependence for defects located in the bulk and in the surface/interface region of a-Si:H. (C) 2004 American Institute of Physics.

Aarts, I. M. P., M. C. M. van de Sanden, et al. (2004). "Analysis of a-Si: H subgap absorption spectra obtained from absolute cavity ringdown absorption spectroscopy using an empirical DOS model." Journal of Non-Crystalline Solids 338-40: 408-411.

The novel thin film cavity ringdown absorption technique in combination with transmission reflection spectroscopy has been employed to obtain absolute absorption spectra of a-Si:H films of 4 nm and 1031 nm thickness between photon energies of 0.7 and 4 eV. Using an empirical density-of-states (DOS) model the absorption spectra have been deconvoluted and the DOS for both films could be determined within conceivable limits. The DOS for the bulk and surface dominated films are clearly different and the dipole matrix elements for the different transitions as well as the resulting dipole matrix function is discussed. (C) 2004 Elsevier B.V. All rights reserved.

Aldener, M., B. Lindgren, et al. (2000). "Cavity Ringdown Laser Absorption Spectroscopy - Nitrogen cation." Physica Scripta 61(1): 62-65.

Two hitherto unanalysed bands (5,1) and (10,5) of the A(2)pi(u)-X(2)Sigma(g)(+) system of the N-2(+) molecule have been studied using the Cavity Ringdown Laser Absorption Spectroscopy (CRLAS) technique. How to distinguish between ionic and neutral lines is discussed and a rotational analysis of the observed bands is performed.

Alexander, A. J. (2004). "Reaction kinetics of nitrate radicals with terpenes in solution studied by cavity ring-down spectroscopy." Chemical Physics Letters 393(1-3): 138-142.

The use of cavity ring-down spectroscopy for kinetic measurements of photo-induced reactions in solution has been demonstrated for the first time. Second-order rate coefficients for reaction of NO3 with terpenes in acetonitrile were determined: (2.93 +/- 0.48) x 10(9) M-1 s(-1) (alpha-pinene), (2.86 +/- 0.35) x 10(9) M-1 s(-1) (beta-pinene), and (1.40 +/- 0.12) x 10(9) M-1 s(-1) (limonene). The rate coefficients were found to be lower than previous measurements in the gas-phase, which we attribute to the onset of a diffusion-controlled limit to the reaction rate in solution. (C) 2004 Elsevier B.V. All rights reserved.

An, K. W., C. H. Yang, et al. (1995). "Cavity Ring-Down Technique And Its Application To The Measurement Of Ultraslow Velocities." Optics Letters 20(9): 1068-1070.

We have developed a new ring-down technique that does not require a shutter to turn a probe laser on and off. With a rapid cavity scan we can measure a simple exponential cavity decay from which a cavity finesse can be found. When the cavity is scanned slowly, the cavity decay exhibits an amplitude modulation, and an analytic expression is derived for this modulation. With this new technique we measured the ultraslow relative velocity of the mirrors (of the order of micrometers per second) as well as the linewidth (similar to 100 kHz) of the probe laser.

Anderson, D. Z., J. C. Frisch, et al. (1984). "Mirror Reflectometer Based On Optical Cavity Decay Time." Applied Optics 23(8): 1238-1245.

Aniolek, K. W., P. E. Powers, et al. (1999). "Cavity ringdown laser absorption spectroscopy with a 1 kHz mid-infrared periodically poled lithium niobate optical parametric generator optical parametric amplifier." Chemical Physics Letters 302(5-6): 555-562.

A cavity ringdown spectrometer is described that employs a novel mid-infrared light source based on periodically poled lithium niobate. The source generates tunable light using the three-step process of optical parametric generation, spectral filtering, and optical parametric amplification. Its use allows for improvements over previous pulsed ringdown measurements including the ability to acquire data rapidly (at 1 kHz) over broad spectral regions tin principle, over the entire 2220-7690 cm(-1) PPLN transparency window) with narrow linewidth (less than or equal to 0.08 cm(-1)). Data are presented that demonstrate performance and support its eventual use in a trace gas sensor. (C) 1999 Elsevier Science B.V. All rights reserved.

Araki, M., H. Linnartz, et al. (2003). "High-resolution electronic spectroscopy of a nonlinear carbon chain radical C6H4+." Journal Of Chemical Physics 118(23): 10561-10565.

A high-resolution gas-phase spectrum of a molecular absorption band around 604 nm is assigned as due to an electronic transition of a nonlinear C6H4+ planar species starting from its (2)A" electronic ground state. The spectrum is observed in direct absorption by cavity ringdown spectroscopy through a supersonic planar discharge through a mixture of acetylene in helium. The spectrum has a clear rotational and K-type structure. This allows an accurate determination of the B and C rotational constants and an estimate for the A rotational constant in ground and electronically excited states. The resolved spectrum of the fully deuterated species C6D4+ has been obtained as well. The results are compared both to the outcome of ab initio geometry optimizations and low-resolution absorption spectra in 6 K neon matrices obtained after mass-selective deposition. (C) 2003 American Institute of Physics.

Ashfold, M. N. R., P. W. May, et al. (2001). "Unravelling aspects of the gas phase chemistry involved in diamond chemical vapour deposition." Physical Chemistry Chemical Physics 3(17): 3471-3485.

We describe laser and mass spectroscopic methods, and related modelling studies, that have been used to unravel details of the gas phase chemistry involved in diamond chemical vapour deposition (CVD) using both H/C (i.e. hydrocarbon/H-2) and H/C/O (e.g. CO2/CH4) gas mixtures, and comment on the relative advantages and limitations of the various approaches. In the case of the more extensively studied hydrocarbon/H-2 systems we pay particular emphasis to investigations (both experimental, and 2- and 3-dimensional modelling) of transient species like H atoms and CH3 radicals, their spatial distributions within the reactor and the ways in which these distributions vary with process conditions, and the insight provided by such investigations into the chemistry underpinning the diamond CVD process. These analyses serve to highlight the rapid thermochemical cycling amongst the various hydrocarbon species in the reactor, such that the gas phase composition in the vicinity of the growing diamond surface is essentially independent of the particular hydrocarbon source gas used. Such applies even to the case of hot filament activated C2H2/H-2 gas mixtures, for which we show that CH, radical formation (hitherto often presumed to involve heterogeneous hydrogenation steps) can be fully explained in terms of gas phase chemistry. Diamond growth using H/C/O-containing gas mixtures has traditionally been discussed in terms of an empirically derived H-C-O atomic phase composition diagram (P. K. Bachmann, D. Leers, H. Lydtin and D. U. Wiechert, Diamond Relat. Mater., 1991, 1, 1). Detailed studies of microwave activated CO2/CH4 gas mixtures, accompanied by simpler zero-dimensional thermochemical modelling of this and numerous other H/C/O-containing input gas mixtures, provide a consistent rationale for the 'no growth', 'diamond growth' and 'non-diamond growth' regions within the H-C-O atomic phase composition diagram.

Ashworth, S. H., B. J. Allan, et al. (2002). "High resolution spectroscopy of the OIO radical: Implications for the ozone-depleting potential of iodine." Geophysical Research Letters 29(10).

[1] The absorption spectrum of iodine dioxide (OIO), obtained at high resolution between 540 and 605 nm by cavity ring-down spectroscopy, exhibits no evidence of coarse rotational structure. Furthermore, a laser induced fluorescence spectrum was not observed when pumping the molecule in this region of the visible spectrum. Ab initio quantum calculations were performed on the ground and first excited states of OIO. The rotational envelopes of the observed absorption bands are very satisfactorily simulated if the lifetime of the excited state is 200 +/- 50 fs, indicating prompt predissociation. Quantum calculations indicate photolysis to I + O-2, rather than O + IO. The estimated photodissociation rate of OIO in daylight ranges from 0.36 to 2.2 s(-1), depending on the choice of absolute cross-section, which explains why OIO has only been observed in the atmosphere after sunset. Photolysis to yield atomic I will enhance the O-3-depleting potential of iodine in the remote marine boundary layer.

Atkinson, D. B. (2003). "Solving chemical problems of environmental importance using cavity ring-down spectroscopy." Analyst 128(2): 117-125.

Cavity ring-down (CRD) is a sensitive variant of traditional absorption spectroscopy that has found increasing use in a number of chemical measurement applications. This review focuses on applications of cavity ring-down spectroscopy that will be of interest to environmental chemists and analytical chemists working on environmental problems. The applications are classified into direct monitoring approaches, indirect analysis methods and ancillary studies and a differentiation is made between field-tested instruments and proof of principle studies.

Atkinson, D. B. and J. W. Hudgens (1997). "Chemical kinetic studies using ultraviolet cavity ring-down spectroscopic detection: Self-reaction of ethyl and ethylperoxy radicals and the reaction O-2+C2H5->C2H5O2." Journal Of Physical Chemistry A 101(21): 3901-3909.

A laser photolysis reactor that uses cavity ring-down spectroscopic (CRDS) detection was characterized and used to measure the rate coefficients of three benchmark reactions of known importance to ethane oxidation. At 295 K and approximately 700 Pa (5.5 Torr) total pressure, we obtained the self-reaction rate coefficients of k = (1.99 +/- 0.44) x 10(-11) cm(3) molecule(-1) s(-1) for C2H5 + C2H5 and k = (7.26 +/- 2.4) x 10(-14) cm(3) molecule(-1) s(-1) for C2H5O2 + C2H5O2 We obtained k = (2.7 +/- 0.3) x 10(-12) cm(3) molecule(-1) s(-1) for the pseudo-first-order association reaction O-2 + C2H5 + AT We also measured the absorption cross sections of the ethyl radical, sigma(220) = (252 +/- 42) x 10(-20) cm(2) molecule(-1) and sigma(222) 2 (206 +/- 42) x 10(-20) cm(2) molecule(-1) Stated uncertainties are 2 sigma. The new rate coefficients agree with those obtained previously by other methods. The agreement confirms that ultraviolet CRDS detection is a viable tool for experimental determinations of gas-phase radical-radical and radical-molecule reaction late coefficients.

Atkinson, D. B. and J. W. Hudgens (1999). "Rate coefficients for the propargyl radical self-reaction and oxygen addition reaction measured using ultraviolet cavity ring-down spectroscopy." Journal Of Physical Chemistry A 103(21): 4242-4252.

By using 193 nm laser photolysis and cavity ring-down spectroscopy to produce and monitor the propargyl radical (CH2CCH), the self-reaction and oxygen termolecular association rate coefficients for the propargyl radical were measured at 295 K between total pressures of 300 Pa and 13300 Pa (2.25 and 100 Torr) in Ar, He, and N-2 buffer gases. The rate coefficients obtained by simple second-order fits to the decay data were observed to vary with the photolytic precursors: allene, propargyl chloride, and propargyl bromide. By using a numerical fitting routine and more comprehensive mechanisms, a distinct rate coefficient for the self-reaction was determined, k(infinity)(C3H3+C3H3) = (4.3 +/- 0.6) x 10(-11) cm(3) molecule(-1) s(-1) at 295 K. This rate coefficient which is a factor of 2.8 times slower than reported previously, was independent of total pressure and buffer choice over the entire pressure range. Other rate coefficients derived during the modeling included k(C3H3+H 665 Pa He) = (2.5 +/- 1.1) x 10(-10) cm(3) molecule(-1) s(-1), k(C3H3+C3H3Cl2) = (7 +/- 4) x 10(-11) cm(3) molecule(-1) s(-1), and k(C3H3+C3H3Br2) = (2.4 +/- 2) x 10(-11) cm(3) molecule(-1) s(-1). The association reaction C3H3+O-2 was found to lie in the falloff region between linear and saturated pressure dependence for each buffer gas (Ar, He, and N-2) between 300 Pa and 13300 Pa. A fit of these data derived the high-pressure limiting rate coefficient k(infinity)(C3H3+O-2) = (2.3 +/- 0.5) x 10(-13) cm(3) molecule(-1) s(-1). Three measurements of the propargyl radical-absorption cross-section obtained sigma(332.5) = (413 +/- 60) x 10(-20) cm(2) molecule(-1) at 332.5 nm. Stated uncertainties are two standard deviations and include the uncertainty of the absorption cross section, where appropriate.

Atkinson, D. B., J. W. Hudgens, et al. (1999). "Kinetic studies of the reactions of IO radicals determined by cavity ring-down spectroscopy." Journal Of Physical Chemistry A 103(31): 6173-6180.

We demonstrate the application of cavity ring-down spectroscopy (CRDS) to the measurement of concentrations of IO radical and of reaction rate coefficients for the reaction systems, IO + IO and IO + NO, using the source reaction, O(P-3) + CSI. By monitoring IO radicals, we obtain the 295 K rate coefficients, k(O + CSI --> IO + CF3) = (5.8 +/- 1.5) x 10(-12) cm(3) molec(-1) s(-1); k(IO + IO) = (1.0 +/- 0.3) x 10(-10) cm(3) molec(-1) s(-1) and k(IO + NO) = (1.9 +/- 0.5) x 10(-12) cm(3) molec(-1) s(-1) at the pressures of 1250 Pa (9.4 Torr) and 4000 Pa (30.1 Torr). For the IO A (2)Pi(3/2) - X (2)Pi(3/2) (2, 0) bandhead at 445.04 nm we have determined an absorption cross-section, sigma = (7.3 +/- 0.7) x 10(-17) cm(2). Error limits indicate the confidence of two standard deviations and propagate the uncertainty in the absorption cross-section.

Atkinson, D. B. and J. L. Spillman (2002). "Alkyl peroxy radical kinetics measured using near-infrared CW-cavity ring-down spectroscopy." Journal Of Physical Chemistry A 106(38): 8891-8902.

A kinetic reactor system is described which couples pulsed laser photolytic production of radicals with continuous laser excitation cavity ring-down spectroscopic detection in the near-infrared (NIR). The atmospherically relevant alkyl peroxy radicals ethyl peroxy (C2H5O2) and methyl peroxy (CH3O2) were monitored via their structured absorbance spectra in the NIR near 1.3 mum. These peroxy radicals were then subjected to kinetic study as proof-of-principle for the new technique. Portions of the absorption spectra for the two radicals are reported which agree well with previously published spectra [Hunziker, H. E.; Wendt, H. R. J. Chem. Phys. 1976, 64, 3488. Pushkarsky, M. B.; Zalyubovsky, S. J.; Miller, T. A. J. Chem. Phys. 2000, 112, 10695]. The absorption cross sections were determined at selected wavelengths using the known self-reaction rate coefficients and observed kinetic data. The absorption cross sections determined are as follows: for two of the maxima in the origin band of C2H5O2, sigma(1317.01) (nm) = sigma(1316.40) (nm) = (3.0 +/- 1.5) x 10(-21) cm(2) molecule(-1), and for a maximum in a sequence band of CH3O2, sigma(1335.07) (nm) = (1.5 +/- 0.8) x 10(-20) cm(2) molecule(-1). Preliminary data for the prototypical peroxy radical cross-reaction between CH3O2 and C2H5O2 is presented. This data supports earlier work [Villenave, E.; Lesclaux, R. J. Phys. Chem. 1996, 100, 14372] which established a pressure independent value of k(CH3O2 + CH3CH2O2) = 2.0 x 10(-13) cm(3) molecule(-1) s(-1) at 298 K. As in most kinetic studies involving peroxy radicals, the accuracy of the reported rate coefficients is influenced by the details of the complex mechanisms used in the fitting. However, in the current studies, specific radical absorption(s) are used to follow each radical's decay, which should improve the precision of the determination.

Awtry, A. R. and J. H. Miller (2002). "Development of a cw-laser-based cavity-ringdown sensor aboard a spacecraft for trace air constituents." Applied Physics B-Lasers And Optics 75(2-3): 255-260.

The progress in the development of a sensor for the detection of trace air constituents to monitor spacecraft air quality is reported. A continuous-wave (cw), external-cavity tunable diode laser centered at 1.55 mum is used to pump an optical cavity absorption cell in cw-cavity ringdown spectroscopy (cw-CRDS). Preliminary results are presented that demonstrate the sensitivity, selectivity and reproducibility of this method. Detection limits of 2.0 ppm for CO, 2.5 ppm for CO2, 1.8 ppm for H2O, 19.4 ppb for NH3, 7.9 ppb for HCN and 4.0 ppb for C2H2 are calculated.

Azarova, V. V., E. L. Giruts, et al. (1994). "Laser Meters Of High-Quality Optical Cavities And Mirrors Parameters." Izvestiya Akademii Nauk Seriya Fizicheskaya 58(2): 91-97.

Baer, D. S., J. B. Paul, et al. (2002). "Sensitive absorption measurements in the near-infrared region using off-axis integrated-cavity-output spectroscopy." Applied Physics B-Lasers And Optics 75(2-3): 261-265.

A novel instrument that employs a high-finesse optical cavity as an absorption cell has been developed for sensitive measurements of gas mixing ratios using near-in rare diode lasers and absorption-spectroscopy techniques. The instrument employs an off-axis trajectory of the laser beam through the cell to yield an effective optical path length of several kilometers without significant unwanted effects due to cavity resonances. As a result, a minimum detectable absorption of approximately 1.4 x 10(-5) over an effective optical path of 4.2km was obtained in a 1.1-Hz detection bandwidth to yield a detection sensitivity of approximately 3.1 x 10(-11) cm(-1) Hz(-1/2). The instrument has been used for sensitive measurements of CO, CH4, C2H2 and NH3

Baev, V. M., T. Latz, et al. (1999). "Laser intracavity absorption spectroscopy." Applied Physics B-Lasers And Optics 69(3): 171-202.

Emission spectra of multimode lasers are very sensitive to spectrally selective extinction in their cavity. This phenomenon allows the quantitative measurement of absorption. The sensitivity of measurements of intracavity absorption grows with the laser pulse duration. The ultimate sensitivity obtained with a cw laser is set by various perturbations of the light coherence, such as quantum noise, Rayleigh scattering, four-wave mixing by population pulsations, and stimulated Brillouin scattering. It depends on the particular laser type used, and on its operative parameters, for example pump power, cavity loss, cavity length, and length of the gain medium. Nonlinear mode-coupling dominates the dynamics of lasers that feature a thin gain medium, such as dye lasers, whereas Rayleigh scattering is more important in lasers with a long gain medium, such as doped fibre lasers, or the Ti:sapphire laser. The highest sensitivity so far has been obtained with a cw dye laser. It corresponds to 70000km effective length of the absorption path. The ultimate spectral resolution is determined by the spectral width of mode emission, which is 0.7 Hz in this dye laser. High sensitivity and high temporal and spectral resolution allow various practical applications of laser intracavity spectroscopy, such as measurements and simulations of atmospheric absorption, molecular and atomic spectroscopy, process control, isotope separation, study of free radicals and chemical reactions, combustion diagnostics, spectroscopy of excited states and nonlinear processes, measurements of gain and of spectrally narrow light emission. Intracavity absorption in single-mode lasers shows enhanced sensitivity as well, although not as high as in multimode lasers.

Bakhirkin, Y. A., A. A. Kosterev, et al. (2004). "Mid-infrared quantum cascade laser based off-axis integrated cavity output spectroscopy for biogenic nitric oxide detection." Applied Optics 43(11): 2257-2266.

Tunable-laser absorption spectroscopy in the mid-IR spectral region is a sensitive analytical technique for trace-gas quantification. The detection of nitric oxide (NO) in exhaled breath is of particular interest in the diagnosis of lower-airway inflammation associated with a number of lung diseases and illnesses. A gas analyzer based on a continuous-wave mid-IR quantum cascade laser operating at similar to5.2 mum and on off-axis integrated cavity output spectroscopy JCOS) has been developed to measure NO concentrations in human breath. A compact sample cell, 5.3 cm. in length and with a volume of <80 cm(3), that is suitable for on-line and off-line measurements during a single breath cycle, has been designed and tested. A noise-equivalent (signal-to-noise ratio of 1) sensitivity of 10 parts in 10(9) by volume (ppbv) of NO was achieved. The combination of ICOS with wavelength modulation resulted in a 2-ppbv noise-equivalent sensitivity. The total data acquisition and averaging time was 15 s in both cases. The feasibility of detecting NO in expired human breath as a potential noninvasive medical diagnostic tool is discussed. (C) 2004 Optical Society of America.

Ball, C. D., M. C. McCarthy, et al. (1999). "Laser spectroscopy of the carbon chains HC7H and HC9H." Astrophysical Journal 523(1): L89-L91.

Strong vibronic bands of the (3)Sigma(u)(-) <-- X(3)Sigma(g)(-) transition of the linear triplet radicals HC7H and HC9H have been measured in the gas phase by cavity ringdown spectroscopy. The origin band of HC7H and the origin and nu(3) bands of HC9H all exhibit well resolved P and R branches. For HC9H, the origin band is within 1 Angstrom of the diffuse interstellar band lambda 5818, yet insufficiently close for positive identification. In both molecules, internal conversion is much more rapid than radiative emission, and fluorescence is not observed. Lower limits on the radiationless lifetime of the upper state of the origin band are determined to be 0.1 ns for HC7H and 0.01 ns for HC9H. Because the origin bands of these two radicals are about equally intense, it should be possible to detect longer members of the series in the gas phase.

Ball, C. D., M. C. McCarthy, et al. (2000). "Cavity ringdown spectroscopy of the linear carbon chains HC7H, HC9H, HC11H, and HC13H." Journal of Chemical Physics 112(23): 10149-10155.

Optical bands from the (3)Sigma(u)(-) <-- X (3)Sigma(g)(-) transition of the linear carbon chains HC7H, HC9H, HC11H, and HC13H have been measured in the gas phase by cavity ringdown spectroscopy. The bands exhibit well resolved P and R branches, which for HC7H are partially rotationally resolved. Comparisons between observed and simulated spectra indicate broadening in excess of that expected from the laser linewidth and Doppler width, suggesting rapid radiationless transitions in roughly 0.1-0.01 ns, a time scale consistent with the absence of observed fluorescence from these molecules. The HC7H and HC9H bands are of nearly equal strength, but those of the shorter chain HC5H are too weak to detect at the 1 ppm level. None of the bands observed here lies sufficiently close to any of the optical diffuse interstellar bands to provide positive identification. (C) 2000 American Institute of Physics. [S0021-9606(00)00423-2].

Ball, C. D., M. C. McCarthy, et al. (2000). "Laboratory detection of a molecular band at lambda 4429." Astrophysical Journal 529(1): L61-L64.

A fairly strong molecular absorption band at 4429.27 +/- 0.04 Angstrom, closely centered on the strongest diffuse interstellar band at 4428.9 +/- 1.4 Angstrom, has been found in a supersonic molecular beam among the products of a discharge through benzene and other hydrocarbons. This agreement in wavelength to a few parts in 10(4) strongly suggests a common carrier. The width of the laboratory band is significantly less than that of the diffuse interstellar hand, but this difference may be the result of the very low rotational temperature in the supersonic beam-possibly as low as 2 K-relative to that of a weakly polar molecule in the diffuse interstellar gas (100-200 K). Several candidate carriers are discussed. Two of the more promising are the allyl cation C3H5+ and the dimethylene allenyl radical C5H5, both bent carbon chains that may be close enough to linear to reconcile the puzzling appearance of P-, Q-, and R-branches in the laboratory band with the five hydrogen atoms suggested by the observed deuterium isotopic shifts.

Ball, S. M. and R. L. Jones (2003). "Broad-band cavity ring-down spectroscopy." Chemical Reviews 103(12): 5239-5262.

Ball, S. M., J. M. Langridge, et al. (2004). "Broadband cavity enhanced absorption spectroscopy using light emitting diodes." Chemical Physics Letters 398(1-3): 68-74.

A broadband variant of cavity enhanced absorption spectroscopy has been demonstrated at visible wavelengths using red and green light emitting diodes. The broadband CEAS spectrum of a mixture of molecular oxygen and water vapour has been recorded with a bandwidth of 60 nm centred at 675 nm. Quantitative amounts of three atmospherically important absorbers (NO3, NO2 and I-2) have also been retrieved from broadband CEAS spectra of laboratory samples at high dilution using spectral fitting techniques adapted from differential optical absorption spectroscopy. (C) 2004 Elsevier B.V. All rights reserved.

Ball, S. M., I. M. Povey, et al. (2001). "Broadband cavity ringdown spectroscopy of the NO3 radical." Chemical Physics Letters 342(1-2): 113-120.

Cavity ringdown spectroscopy (CRDS) has been demonstrated using a broadband (20 nm) laser source and a two-dimensional clocked detector array. Absorption spectra of dilute samples (50-500 parts per trillion) of the nitrate radical, NO3, have been obtained between 650 and 670 nm by monitoring simultaneously the time and wavelength resolved output of a ringdown cavity. The potential of broadband CRDS for making measurements on samples containing multiple absorbers (e.g., atmospheric samples) is shown by applying analysis methods from differential optical absorption spectroscopy to quantify the NO, concentration in the presence of nitrogen dioxide impurities. (C) 2001 Elsevier Science B.V. All rights reserved.

Barmenkov, Y. O., A. Ortigosa-Blanch, et al. (2004). "Time-domain fiber laser hydrogen sensor." Optics Letters 29(21): 2461-2463.

We report a novel scheme for a fiber-optic hydrogen sensor based on an erbium-doped fiber laser with a palladium-coated tapered fiber within the laser cavity. The tapered fiber acts as a hydrogen-sensing element. When the sensing element is exposed to a hydrogen atmosphere, its attenuation decreases, changing the cavity losses and leading to a modification of the laser transient. The hydrogen concentration is obtained by simple measurement of the buildup time of the laser. This technique translates the measurement of hydrogen concentration into the time domain, and it can be extended to many intensity-based fiber sensors. Relative variations in the buildup time of up to 55% at an increase of the hydrogen concentration from 0 to 10% are achieved with a resolution of better than 0.1%. (C) 2004 Optical Society of America.

Barry, H. R., B. Bakowski, et al. (2000). "OH detection by absorption of frequency-doubled diode laser radiation at 308 nm." Chemical Physics Letters 319(1-2): 125-130.

Radiation at 308 nm has been obtained by frequency doubling the output of a commercial diode laser cooled to 165 K. A single pass through a crystal of LiIO3 converted 1 mW of 616 nm radiation to 50 pW of UV, and this was used to detect the OH radical in absorption in a flow tube. Possible extensions of the method for detection of OH in the atmosphere are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

Bean, B. D., A. K. Mollner, et al. (2003). "Cavity ringdown spectroscopy of cis-cis HOONO and the HOONO/HONO2 branching ratio in the reaction OH+NO2+M." Journal Of Physical Chemistry A 107(36): 6974-6985.

The termolecular association reaction OH + NO2 + M was studied in a low-pressure discharge flow reactor, and both HONO2 and HOONO products were detected by infrared cavity ringdown spectroscopy (IR-CRDS). The absorption spectrum of the fundamental nu(1) band of the cis-cis isomer of HOONO (pernitrous or peroxynitrous acid) was observed at 3306 cm(-1), in good agreement with matrix isolation studies and ab initio predictions. The rotational contour of this band was partially resolved at I cm-1 resolution and matched the profile predicted by ab initio calculations. The integrated absorbances of the nu(1) bands of the cis-cis HOONO and HONO2 products were measured as a function of temperature and pressure. These were converted to product branching ratios by scaling the experimentally observed absorbances with ab initio integrated cross sections for HOONO and HONO2 computed at the CCSD(T)/cc-pVTZ level. The product branching ratio for cis-cis HOONO to HONO, was 0.075 +/- 0.020(2sigma) at room temperature in a 20 Torr mixture of He/Ar/N, buffer gas. The largest contribution to the uncertainty is from the ab initio ratio of the absorption cross sections, computed in the double harmonic approximation, which is estimated to be accurate to within 20%. The branching ratio decreased slightly with temperature over the range 270 to 360 K at 20 Torr. Although trans-perp HOONO was not observed, its energy was computed at the CCSD(T)/cc-pVTZ level to be E-0 = +3.4 kcal/mol relative to the cis-cis isomer. Statistical rate calculations showed that the conformers of HOONO should reach equilibrium on the time scale of this exeriment. These results suggested that essentially all isomers had converted to cis-cis HOONO; thus, the reported branching ratio is a lower bound for and may represent the entire HOONO yield.

Benedikt, J., K. G. Y. Letourneur, et al. (2002). "Plasma chemistry during deposition of a-C: H." Diamond And Related Materials 11(3-6): 989-993.

The different dissociation products (C, C-2 CH and C2H) from C2H2 dissociation in a remote Ar/C2H2 plasma were measured using Cavity Ring Down Spectroscopy (CRDS). Whereas the radicals C, C-2 and CH were spectrally identified, in the region where C2H absorption is usually assigned (260-290 nm) only broadband absorption was observed. Suggestions are given on how to explain the broadband absorption, but as yet no clear identification has been made and no species assigned to it. (C) 2002 Elsevier Science B.V. All rights reserved.

Berden, G., R. Engeln, et al. (1998). "Cavity-ring-down spectroscopy on the oxygen A band in magnetic fields up to 20 T." Physical Review A 58(4): 3114-3123.

Rotationally resolved spectra of the b (1)Sigma(g)(+) (v = 0) <-- X (3)Sigma(g)(-) (v = 0) band of molecular oxygen are recorded by cavity-ring-down (CRD) spectroscopy in magnetic fields up to 20 T. Measurements are performed in a 3-cm-long cavity, placed in the homogeneous field region inside a Bitter magnet. CRD absorption spectra are measured with linearly and circularly polarized light, leading to different Delta M selection rules in the molecular transition, thereby aiding in the assignment of the spectra. Dispersion spectra are obtained by recording the rate of polarization rotation, caused by magnetic circular birefringence, using the polarization-dependent CRD detection scheme. Matrix elements for the Hamiltonian and for the transition moment are presented on a Hund's case a basis in order to calculate the frequencies and intensities of the rotational transitions of the oxygen A band in a magnetic field. All spectral features can be reproduced, even in the highest magnetic fields. The molar magnetic susceptibility of oxygen is calculated as function of the magnetic-field strength and the temperature, and a discussion on the alignment of the oxygen molecules in the magnetic field is given. [S1050-2947(98)06710-9].

Berden, G., R. Peeters, et al. (1999). "Cavity-enhanced absorption spectroscopy of the 1.5 mu m band system of jet-cooled ammonia." Chemical Physics Letters 307(3-4): 131-138.

Absorption spectra of rotationally cold ammonia ((NH3)-N-14) molecules have been recorded in the 6400-6630 cm(-1) region, using the cavity-enhanced absorption technique in combination with a slit-nozzle expansion. Two perpendicular rovibrational bands have been identified: the nu(1) + nu(3) band at 6609 cm(-1), and a 'new' band at 6557 cm(-1) which is tentatively assigned to a transition into the \l\ = 2 component of the nu(1) + 2 nu(4) state. (C) 1999 Elsevier Science B.V. All rights reserved.

Berden, G., R. Peeters, et al. (2000). "Cavity ring-down spectroscopy: Experimental schemes and applications." International Reviews In Physical Chemistry 19(4): 565-607.

Cavity ring-down (CRD) spectroscopy is a direct absorption technique, which can be performed with pulsed or continuous light sources and has a significantly higher sensitivity than obtainable in conventional absorption spectroscopy. The CRD technique is based upon the measurement of the rate of absorption rather than the magnitude of absorption of a light pulse confined in a closed optical cavity with a high Q factor. The advantage over normal absorption spectroscopy results from, firstly, the intrinsic insensitivity to light source intensity fluctuations and, secondly, the extremely long effective path lengths (many kilometres) that can be realized in stable optical cavities. In the last decade, it has been shown that the CRD technique is especially powerful in gas-phase spectroscopy for measurements of either strong absorptions of species present in trace amounts or weak absorptions of abundant species. In this review, we emphasize the various experimental schemes of CRD spectroscopy, and we show how these schemes can be used to obtain spectroscopic information on atoms, molecules, ions and clusters in many environments such as open air, static gas cells, supersonic expansions, flames and discharges.

Biennier, L., D. Romanini, et al. (2000). "Structure and rovibrational analysis of the [O-2((1)Delta(g))(v=0)](2)<-[O-2((3)Sigma(-)(g))(v=0)](2) transition of the O-2 dimer." Journal Of Chemical Physics 112(14): 6309-6321.

The rotationally resolved absorption spectrum of the O-2 dimer involving the [O-2((1)Delta(g))(v=0)](2)<--[O-2((3)Sigma(g)(-))(v=0)](2) transition has been recorded near 632.6 nm by continuous wave Cavity Ring Down Spectroscopy in a supersonic slit jet expansion of pure O-2. A quadratic dependence of the absorption in the jet versus the stagnation pressure is observed. A rotational temperature of 12 K is derived from the (O-2)(2) rotational analysis. The high spectral resolution of the CW-CRDS measurements limited by the residual Doppler broadening in the jet and the low rotational temperature allow the first rotational analysis in this open-shell complex. The same spectrum was also recorded by Intracavity Laser Absorption Spectroscopy and the comparison of the performances of the two methods is discussed. Among more than 600 lines measured between 15 800 and 15 860 cm(-1) from the CW-CRDS spectrum, 40 were assigned to the P-R(0), (R)Q(0), and R-R(0) branches of two subbands associated with B-1(-)<-- A(1)(+) and A(1)(+)<-- B-1(-) transitions between the ground and excited rovibrational levels, labeled following the G(16) permutation inversion representation. Forty five lines were assigned to P-P(2), (P)Q(2), and R-P(2) branches of two subbands associated with B-1(-)<-- A(1)(+) and A(1)(+)<-- B-1(-) transitions. The subbands centered at 15 808.401(49) [A(1)(+)<-- B-1(-)] and 15 813.134(37) cm(-1) [B-1(-)<-- A(1)(+)] for those arising from K=0, and at 15 812.656(20) [A(1)(+)<-- B-1(-)] and 15 818.277(35) [B-1(-)<-- A(1)(+)] when arising from K=2, are analyzed considering (O-2)(2) as a slightly asymmetric prolate top. The rotational analysis of the two K=0 subbands leads to very close values of the effective rotational constant, B-p=(B+C)/2, for both A(1)(+) and B-1(-) levels: 0.095 cm(-1) for the [O-2((3)Sigma(g)(-))(v=0)](2) lower states and 0.063 cm(-1) for the [O-2((1)Delta(g))(v=0)](2) excited states, in close agreement with theoretical values. The H geometry is confirmed as the most stable for the ground electronic singlet state. A distance between the two monomers of 6.1 a(0) and 7.5 a(0) is derived for the ground and excited singlet states. Similar results are obtained from the two K=2 subbands. A vibrational assignment is given for the two rotationally analyzed subbands (K=0) and proposed for the main features of the whole band. (C) 2000 American Institute of Physics. [S0021-9606(00)01614-7].

Biennier, L., F. Salama, et al. (2003). "Pulsed discharge nozzle cavity ringdown spectroscopy of cold polycyclic aromatic hydrocarbon ions." Journal Of Chemical Physics 118(17): 7863-7872.

The gas-phase electronic absorption spectra of the naphthalene (C10H8+) and acenaphthene (C12H10+) cations have been measured in the visible range in a free jet planar expansion in an attempt to collect data in an astrophysically relevant environment. The direct absorption spectra of two out of four bands measured of the gas-phase cold naphthalene cation along with the gas-phase vibronic absorption spectrum of the cold acenaphthene cation are reported for the first time. Direct absorption spectra of their van der Waals complexes with argon are also reported for the first time. The study has been carried out using the ultrasensitive and versatile technique of cavity ringdown spectroscopy (CRDS) coupled to a pulsed discharge slit nozzle (PDN). The new PDN-CRDS set up is described and its characteristics are evaluated. The direct-absorption spectra of the polycyclic aromatic hydrocarbon (PAH) ions are discussed and compared to the gas-phase and solid-phase data available in the literature. The analysis of the results show that cold, free flying PAH ions are generated in the argon discharge primarily through soft Penning ionization. This enables the intrinsic band profiles to be measured, a key requirement for astrophysical applications. (C) 2003 American Institute of Physics.

Biennier, L., F. Salama, et al. (2004). "Multiplex integrated cavity output spectroscopy of cold PAH cations." Chemical Physics Letters 387(4-6): 287-294.

Multiplex Integrated Cavity Output Spectroscopy (MICOS) is a new cavity-enhanced absorption method that allows the use of broadband dye nanosecond pulsed laser sources and offers a sensitivity equivalent to CRDS. MICOS has been coupled to a pulsed discharge slit nozzle to measure the spectra of the cold naphthalene (C10H8+), acenaplithene (C12H10divided by) and pyrene (C16H10divided by) cations in the gas phase. A femtosecond relaxation timescale is measured for the D-5 <-- D-0 (0-0) transition of C16H10divided by. Spectra recorded at high plasma energies also show evidence of fragmentation. The CH radical is observed and carbon nanoparticles are generated in the plasma. Published by Elsevier B.V.

Bilger, H. R., P. V. Wells, et al. (1994). "Origins Of Fundamental Limits For Reflection Losses At Multilayer Dielectric Mirrors." Applied Optics 33(31): 7390-7396.

Fundamental limits on reflection losses are set by internal material losses associated with the Urbach tail near a band gap and by thermodynamic density fluctuations in fabrication. In materials such as SiO2 and TiO2, these limits are of the order of parts in 10(9). The current quality of supercavity mirrors, in contrast to that of optical fibers, is still far from these limits because of purely technological limitations in surface preparation and in the reduction of impurity levels. Overcoming these would greatly benefit, for example, Fabry-Perot interferometers, ring lasers, and gravitational wave detectors.

Billardon, M., M. E. Couprie, et al. (1991). "Fabry-Perot Effects In The Exponential Decay And Phase-Shift Reflectivity Measurement Methods." Applied Optics 30(3): 344-351.

The exponential decay and phase shift reflectivity measurement methods are examined for a real optical cavity, i.e., one that includes mechanical vibrations and light source fluctuations in wavelength and amplitude. We compare the two methods and examine the problems inherent in each and present methods for overcoming these. Both methods are shown to be excellent for measuring high reflectivity cavity losses (particularly for the free electron laser case) although suitable precautions should be taken.

Birza, P., D. Khoroshev, et al. (2003). "Lifetime broadening in the gas phase B(over-tilde)(2)Pi <- X(over-tilde)(2)Pi electronic spectrum of C8H." Chemical Physics Letters 382(3-4): 245-248.

The origin band of the B(2)Pi(3/2) <-- X(2)Pi(3/2) electronic transition of linear C8H was recorded in a planar supersonic expansion by a cw cavity ring-down spectrometer. The C8H radical was produced using a discharge through a C2H2/He mixture inside a pulsed slit nozzle. Despite the fact that the resolution of the spectrometer is 350 MHz, which is 3-4 times higher than the separation of rotational lines in this band, the rotational structure was not resolved. It is concluded that the rotational lines are broadened by rapid radiationless transitions from the excited electronic state. Simulations of the spectrum give an estimate of 0.8 cm(-1) Lorentzian linewidth which corresponds to similar to7 ps lifetime in the excited B(2)Pi(3/2) electronic state. (C) 2003 Elsevier B.V. All rights reserved.

Birza, P., T. Motylewski, et al. (2002). "Cw cavity ring down spectroscopy in a pulsed planar plasma expansion." Chemical Physics 283(1-2): 119-124.

A cw cavity ring down spectrometer has been constructed with the aim to record electronic spectra of rotationally cold carbon chain radicals at high spectral resolution in direct absorption. The radicals are generated in a discharge of a high pressure gas pulse of acetylene in helium in a multilayer slit nozzle. A passive cavity mode locking scheme is used to handle refractive index changes inside the cavity caused by gas pulse and plasma fluctuations. The performance is demonstrated on the rotationally resolved origin band spectrum of the A(2)Pi(g) - X(2)Pi(u) electronic transition of the triacetylene cation, HC6H+, around 16654.7 cm(-1). (C) 2002 Elsevier Science B.V. All rights reserved.

Bolot'ko, L. M., V. I. Pokatashkin, et al. (2001). "Laser absorption spectrometer based on a passive cavity." Journal Of Optical Technology 68(1): 41-43.

A simple system has been implemented for a laser absorption spectrometer based on a passive cavity formed by standard interference mirrors having high reflectance in the 550-750 and 750-300-nm regions and fabricated using ordinary electron-beam deposition. The real reflectances of the mirrors and the ratio between their reflectance and transmittance have been determined. It is shown that the maximum reflectance does not exceed 99.4% and that up to 1% of the radiation incident on the mirrors is scattered and absorbed in the multilayer structure of the dielectric layers and their substrate. The highest-sensitivity parameters of the laser cavity spectrometer based on such mirrors spectrometer are established, acid it is demonstrated that the spectrometer can be used to experimentally detect and investigate trace quantities of a substance in gas-phase systems. (C) 2001 The Optical Society of America.

Boogaarts, M. G. H., P. J. Bocker, et al. (2000). "Cavity ring down detection of SiH3 on the broadband (A)over-tilde (2)A '(1) <- (X)over-tilde (2)A(1) transition in a remote Ar-H-2-SiH4 plasma." Chemical Physics Letters 326(5-6): 400-406.

Here we report on the use of the cavity ring down (CRD) technique for the detection of the silyl radical SiH3 on the broadband (A) over tilde (2)A(1)' <-- (X) over tilde (2)A(1) transition around 215 nm. SiH3 has been detected in a remote Ar-H-2-SiH4 plasma during hydrogenated amorphous silicon (a-Si:H) thin film growth. The measurements demonstrate the capability of CRD to measure small broadband absorptions in the deep UV in the hostile environment of a deposition plasma. The SiH3 absorption shows an expected dependence on the SiH4 precursor flow and correlates well with the a-SiH growth rate. The observed absorptions correspond with SiH3 densities in the range 2-13 x 10(18) m(-3), which is at least two orders of magnitude above the estimated SiH3 detection limit. (C) 2000 Elsevier Science B.V. All rights reserved.

Boogaarts, M. G. H. and G. Meijer (1995). "Measurement Of The Beam Intensity In A Laser-Desorption Jet-Cooling Mass-Spectrometer." Journal Of Chemical Physics 103(13): 5269-5274.

In a laser desorption jet-cooling molecular beam spectrometer the concentration of translationally and internally cooled laser desorbed organic molecules that can be achieved is experimentally determined. Sensitive direct absorption detection of laser desorbed jet-cooled diphenylamine (DPA) via cavity ring down (CRD) spectroscopy on the S-1<--S-0 transition around 308 nm is used to measure the line-integrated absolute absorption of the pulse of laser desorbed DPA molecules. The absolute cross section for the various vibrational bands of the electronic transition that is used, is determined in a separate two-color ionization experiment. It is concluded that the optimum beam intensity that is obtained with laser desorption is comparable to the beam intensity that is obtained in the same spectrometer by conventional seeding of the desired species at a partial pressure of 10(-4). (C) 1995 American Institute of Physics.

Booth, J. P., G. Cunge, et al. (2000). "Ultraviolet cavity ring-down spectroscopy of free radicals in etching plasmas." Chemical Physics Letters 317(6): 631-636.

Many reactive species of interest in technological plasmas absorb light in the UV spectral region (200-300 nm). Measurement of these weak absorbances (typically 10(-2)-10(-4) for a single pass) allows us to determine their absolute concentration. Low-resolution absorption spectra of these systems have previously been obtained by broad-band absorption spectroscopy. Here we present spectra obtained using laser cavity ring-down spectroscopy, which has much higher spectral resolution, and potentially higher sensitivity. Spectra were obtained for CF, CF2, AlF and SiF2 radicals in capacitively-coupled radio-frequency plasmas in fluorocarbon gases. This technique offers the possibility of real-time (1 s) absolute concentration measurements during wafer processing. (C) 2000 Elsevier Science B.V. All rights reserved.

Brown, R. S., I. Kozin, et al. (2002). "Fiber-loop ring-down spectroscopy." Journal Of Chemical Physics 117(23): 10444-10447.

Pulsed, visible and near-infrared laser light is coupled into an optical fiber, which is wound into a loop using a fiber splice connector. The light pulses traveling through the fiber-loop are detected using a photomultiplier detector. It is found that once the light is coupled into the fiber it experiences very little loss and the light pulses do a large number of round trips before their intensity is below the detection threshold. Measurements of the loss-per-pass and of the ring-down time allow for characterization of the different loss mechanisms of the light pulses in the fiber and splice connector. This method resembles "cavity ring-down absorption spectroscopy" and is well suited to characterize low-loss processes in fiber optic transmission independent from power fluctuations of the light source. It is demonstrated that by measuring the ring-down times one can accurately determine the absolute transmission of an optical fiber and of the fiber connector. In addition it is demonstrated that the technique is useful as an absorption spectroscopic technique of very small sample volumes. A solution of an organic dye was placed between the fiber ends instead of the usual index matching fluid, and an absorption spectrum of 7x10(-15) mol of the dye 1,1(')-diethyl-4,4(')-dicarbocyanine iodide in 7x10(-12) L of dimethylsulfoxide was recorded. (C) 2002 American Institute of Physics.

Brown, S. S. (2003). "Absorption spectroscopy in high-finesse cavities for atmospheric studies." Chemical Reviews 103(12): 5219-5238.

Brown, S. S., A. R. Ravishankara, et al. (2000). "Simultaneous kinetics and ring-down: Rate coefficients from single cavity loss temporal profiles." Journal Of Physical Chemistry A 104(30): 7044-7052.

Cavity ring-down spectroscopy is a recently developed technique for highly sensitive detection of atomic and molecular absorptions. Here, we demonstrate the application of this technique to the measurement of kinetics that occur on the same time scale as the loss of light intensity from an optical cavity. We report rate constants for the reactions NO + NO3 --> 2NO(2) and OH + HNO3 --> H2O + NO3 at 296 K, measured as a test of this method. Observed ring-down profiles with a changing absorber concentration match calculated profiles, and fits to these profiles produce rate constants that agree with literature values to within the uncertainty of the measurements. The technique is general and should provide a simple means of measuring kinetic parameters for fast reactions. We also note the possible uses of this method for a variety of kinetics experiments and the outlook for future improvements.

Brown, S. S., H. Stark, et al. (2002). "Simultaneous in situ detection of atmospheric NO3 and N2O5 via cavity ring-down spectroscopy." Review Of Scientific Instruments 73(9): 3291-3301.

This article describes the application of cavity ring-down spectroscopy (CaRDS) to the simultaneous concentration measurement of nitrate radical, NO3, and dinitrogen pentoxide, N2O5, in the ambient atmosphere. The sensitivity for detection of both NO3 and N2O5 is 0.5 pptv (2sigma) for a 5 s integration, comparable to or better than previous measurements of NO3 (e.g., via DOAS), but with significantly better time resolution. Furthermore, direct measurement of N2O5 represent a previously unavailable capability. Concentrations of both species are measured simultaneously in two separate flow systems and optical cavities pumped by the same pulsed dye laser at 662 nm. One of the flow systems remains at ambient temperature for detection of NO3, while the other is heated to 80 degreesC to induce thermal decomposition of N2O5 providing a measurement of the sum of the NO3 and N2O5 concentrations. This article outlines a series of laboratory and field tests of the instrument's performance. Important considerations include signal acquisition, zero measurements, aerosol interference, flow system losses, and the conversion efficiency for N2O5 thermolysis to NO3. We describe the limitations of this method and show how they can be quantified and accounted for in field measurements. (C) 2002 American Institute of Physics.

Brown, S. S., H. Stark, et al. (2001). "In-situ measurement of atmospheric NO3 and N2O5 via cavity ring-down spectroscopy." Geophysical Research Letters 28(17): 3227-3230.

We report the application of cavity ring-down spectroscopy (CaRDS), a high-sensitivity absorption technique, to the in-situ detection of both NO, and N2O5 in ambient air. The detection limit for NO, measuring absorption in its strong, 662-nm band, is 0.3 pptv at STP (50 s integration time). Heating the air flow through the inlet thermally dissociates N2O5 to yield NO3, whose detection gives the ambient concentration of N2O5. The instrument was successfully field tested in March-April, 2001 at a site in the tropospheric boundary layer in Boulder, Colorado. This study is the first fast-response (5 s - I min), in-situ detection of NO3. It is also the first in-situ detection of N2O5 and the first observation of this species in the troposphere. Both NO, and N2O5 showed considerable temporal variability, highlighting the need for a fast-response instrument.

Brown, S. S., H. Stark, et al. (2002). "Cavity ring-down spectroscopy for atmospheric trace gas detection: application to the nitrate radical (NO3)." Applied Physics B-Lasers And Optics 75(2-3): 173-182.

Cavity ring-down spectroscopy is a relatively new and quite sensitive technique for the measurement of gas-phase optical extinction. It holds the potential for simple, direct and sensitive measurement of the concentrations of a variety of trace gases in the atmosphere. For example, detection of the nitrate radical, NO3. and its companion, dinitrogen pentoxide, N2O5, has been demonstrated with a sensitivity of 0.25 pptv (1sigma). This paper considers several of the requirements for the application of cavity ring-down spectroscopy to concentration measurements of trace gases in ambient air. These include detection sensitivity, measurement of an accurate zero in the presence of competing absorbers, cavity stability and mirror cleanliness, laser line-width effects, saturation effects, Rayleigh scattering, the influence of atmospheric aerosols and sampling issues for reactive species. Examples drawn from our work on NO3 and N2O5 detection in the field illustrate these considerations.

Brown, S. S., H. Stark, et al. (2003). "Nitrogen oxides in the nocturnal boundary layer: Simultaneous in situ measurements of NO3, N2O5, NO2, NO, and O-3." Journal Of Geophysical Research-Atmospheres 108(D9).

[1] We report the first simultaneous in situ observation of a suite of compounds important in nocturnal nitrogen oxide chemistry. Measurements took place at a ground site near Boulder, Colorado, during the fall of 2001. Chemical measurements included NO3, N2O5, NO, NO2 and O-3; meteorological data were also available. The concentrations of NO3 and N2O5 showed large dynamic ranges that were consistent with variations in NO2 and NO and with shifts in meteorological conditions at this site. The observed ratio of N2O5 to NO3 agreed with the ratio calculated from the measured NO2 concentration and the temperature-dependent equilibrium constant. In addition, NO3 and N2O5 showed large short-term variability that may indicate inhomogeneously mixed source and sink compounds and/or deposition at this ground-based measurement site. Finally, N2O5 reached a peak concentration of nearly 3 ppbv under polluted conditions and accounted for an appreciable fraction of the total concentration of measured nitrogen oxide species.

Brown, S. S., R. W. Wilson, et al. (2000). "Absolute intensities for third and fourth overtone absorptions in HNO3 and H2O2 measured by cavity ring down spectroscopy." Journal Of Physical Chemistry A 104(21): 4976-4983.

Photodissociation of nitric acid and hydrogen peroxide via high-lying O-H overtone absorptions in the visible may act as a source of OH radicals in the atmosphere. We have used cavity ring down spectroscopy to measure the absorption cross sections for the third (4 nu(OH)) and fourth (5 nu(OH)) overtone transitions in these molecules. The integrated cross sections are (2.25 +/- 0.15) x 10(-21) and (2.57 +/- 0.24) x 10(-22) cm(2) molecule(-1) cm(-1) for 4 nu(OH) and 5 nu(OH) in nitric acid, respectively, and (4.58 +/- 0.39) x 10(-21) and (5.67 +/- 0.52) x 10(-22) cm(2) molecule(-1) cm(-1) for 4 nu(OH) and 5 nu(OH) in hydrogen peroxide. For both molecules, our report is the first direct intensity measurement for 5 nu(OH). the lowest dissociative overtone transition. We compare our values for the lower overtones to those from previous studies, where available. Our measured cross sections suggest that the contribution of direct overtone excitation to the atmospheric photodissociation of HNO3 and H2O2 is small but not completely negligible.

Bucher, C. R., K. K. Lehmann, et al. (2000). "Doppler-free nonlinear absorption in ethylene by use of continuous-wave cavity ringdown spectroscopy." Applied Optics 39(18): 3154-3164.

We report what we believe to be the first systematic study of Doppler-free, nonlinear absorption by use of cavity ringdown spectroscopy. We have developed a variant of cavity ringdown spectroscopy for the mid-infrared region between 9 and 11 mu m, exploiting the intracavity power buildup that is possible with continuous-wave lasers. The infrared source consists of a continuous-wave CO2 laser with 1-mW tunable infrared sidebands that couple into a high-finesse stable resonator. me tune the sideband frequencies to observe a saturated. Doppler-free Lamb dip in the v(7), 11(1,10) <-- 11(2,10) rovibrational transition of ethylene (C2H4). Power studies of the Lamb dip are presented to examine the intracavity effects of saturation on the Lamb-dip linewidth, the peak depth, and the broadband absorption. (C) 2000 Optical Society of America. OCIS codes: 230.5750, 300.6190, 300.6320, 300.6340, 300.6420, 300.6460.

Bulatov, V., M. Fisher, et al. (2002). "Aerosol analysis by cavity-ring-down laser spectroscopy." Analytica Chimica Acta 466(1): 1-9.

The cavity-ring-down technique was applied for aerosol detection. The experimental set-up was based on a pulsed dye laser pumped with the third harmonic of an Nd:YAG laser. Validation of the method was performed using calibrated aerosol flows, all under ambient conditions. The method was exemplified with non-absorbing aerosols, such as NaCl and CuCl2.2H(2)O, of various sizes and concentrations. The results were used for the evaluation of the corresponding aerosol extinction coefficients as a function of size, shape and index of refraction. The thus obtained aerosol extinction efficiencies were compared to theoretical models. Good agreement with theory was observed for NaCl aerosols, while the results for CUCl2.2H(2)O particulates required averaging over particle size and over the orientation dependent index of refraction. The actual sensitivity currently achieved was as low as an extinction coefficient of 8 x 10(-8) cm(-1), which means detection capability of about six water micro-particulates per cm(3). The ultimate theoretical performance of this method for aerosol detection was estimated as an extinction coefficient of 1.4 x 10(-12) cm(-1), corresponding to about 100 micro-particulates per m(3). These figures indicate that this method has the potential to become one of the most sensitive on-line analytical technique for aerosol detection and quantification. (C) 2002 Elsevier Science B.V. All rights reserved.

Bulatov, V., A. Khalmanov, et al. (2003). "Study of the morphology of a laser-produced aerosol plume by cavity ringdown laser absorption spectroscopy." Analytical And Bioanalytical Chemistry 375(8): 1282-1286.

Cavity ring-down laser absorption spectroscopy (CRLAS) was applied for the first time to detection and characterization of laser breakdown generated aerosols. The method provided time-resolved morphological information on the aerosol plume, which is of importance in laser ablation (LA) and deposition, in laser-induced breakdown spectroscopy (LIBS) analysis, and in laser ablation inductively coupled plasma (LA-ICP) methods. This method provides sensitive detection of a variety of aerosols produced under ambient conditions. The morphological investigation revealed that the aerosol density has a reproducible pattern as a function of distance from the surface, although its details depend on time, on geometrical parameters and on the surface characteristics.

Campargue, A., L. Biennier, et al. (1999). "High resolution absorption spectroscopy of the nu(1)=2-6 acetylenic overtone bands of propyne: Spectroscopy and dynamics." Journal Of Chemical Physics 111(17): 7888-7903.

The rotationally resolved n nu(1) (n=2-6) overtone transitions of the CH acetylenic stretching of propyne (CH3-C equivalent to C-H) have been recorded by using Fourier transform spectroscopy (n=2), various intracavity laser absorption spectrometers (n=3, 4, and 6) and cavity ring down spectroscopy (CRDS) (n=5). The 2 nu(1), 3 nu(1), and 6 nu(1) bands exhibit a well-resolved and mostly unperturbed J-rotational structure, whose analysis is reported. The 5 nu(1) band recorded by pulsed CRDS shows an unresolved rotational envelope. In the region of 12 700 cm(-1), an anharmonic interaction is confirmed between 4 nu(1) and 3 nu(1)+nu(3)+nu(5). The band at a higher wave number in this dyad exhibits a partly resolved K-structure, whose analysis is reported. The mixing coefficient of the two interacting states is determined consistently using different procedures. The 1/35 anharmonic resonance evidenced in the 4 nu(1) manifold induces weaker intensity borrowing from the 2 nu(1) and 3 nu(1) levels to the nu(1)+nu(3)+nu(5) and 2 nu(1)+nu(3)+nu(5) level, respectively, which have been predicted and identified. Several hot bands around the 2 nu(1), 3 nu(1), and 3 nu(1)+nu(3)+nu(5) bands arising from the nu(9)=1 and nu(10)=1 and 2 bending levels are identified and rotationally analyzed, also leading to determine x(1,9) [-20.3(3) cm(-1)], x(1,10) [-1.7975(75) cm(-1)], and x(3,10) [-6.56 cm(-1)]. The J-clumps of the P and R branches in the 6 nu(1) band at 18 499 cm(-1) show a Lorentzian homogeneous profile mostly J-independent with an average full width at half maximum (FWHM) of 0.17 cm(-1), attributed to arising from the intramolecular vibrational energy redistribution towards the bath of vibrational states. A detailed comparative examination of the fine structure in all investigated n nu(1) (n=2 to 7) overtone bands and the similar behavior of the cold and hot bands arising from nu(10)=1 definitively suggests that a highly specific low-order anharmonic coupling, still unidentified, dominates the hierarchy of interaction mechanisms connecting the n nu(1) levels to the background states. (C) 1999 American Institute of Physics. [S0021-9606(99)01334-3].

Campargue, A., A. Charvat, et al. (1994). "Absolute Intensity Measurement Of Co2 Overtone Transitions In The Near-Infrared." Chemical Physics Letters 223(5-6): 567-572.

The absorption spectra of three near-infrared bands of (CO2)-C-12-O-16 assigned to 00051, 10051 and 10052 have been obtained by intracavity laser absorption spectroscopy with a Ti: sapphire laser. Different procedures have been used to obtain absolute measurement of the intensity of the rotational lines and then to deduce the band intensity. Comparison with previous conflicting photoacoustic measurements is discussed. The values obtained could serve as secondary reference standards for other intensity measurements of weak absorptions in the near-infrared range.

Campargue, A., D. Romanini, et al. (1998). "Measurement of SiH2 density in a discharge by intracavity laser absorption spectroscopy and CW cavity ring-down spectroscopy." Journal Of Physics D-Applied Physics 31(10): 1168-1175.

Two highly sensitive and quantitative absorption techniques have been applied to the detection of SiH2 in an argon-5% silane DC discharge, the new method of CW cavity ring-down spectroscopy (CWCRDS) and intracavity laser absorption spectroscopy (ICLAS). Doppler-limited absorption lines of the (A) over tilde B-1(1)(020) <-- (X) over tilde (1)A(1)(000) transition around 580 nm could be observed. By using the rotational constants and the electronic transition moment available in the literature, we have calculated the line intensity of some specific rovibronic transitions from which we deduced the concentration of SiH2 in the discharge to be about 10(10) cm(-3). Taking into account the signal-to-noise ratio, concentrations as small as a few times 10(8) cm(-3) can be detected by both methods. We also observed a weak broadband absorption of several 10(-7) cm(-1) due to the dust particles formed in the plasma volume, which for particles of 1 nm diameter would correspond to a few times 10(9) cm(-3). The performances of ICLAS and CWCRDS are compared.

Casaes, R., R. Provencal, et al. (2002). "High resolution pulsed infrared cavity ringdown spectroscopy: Application to laser ablated carbon clusters." Journal Of Chemical Physics 116(15): 6640-6647.

We report the design and performance of a tunable, pulsed high resolution mid infrared cavity ringdown spectrometer. Stimulated Raman scattering in H-2/D-2 is used to downconvert the output of a SLM Alexandrite ring laser (720-800 nm) to the mid infrared (3-8 mum). The infrared frequency bandwidth was determined to be 90+/-5 MHz from measurements of Doppler broadened OCS transitions at 5 mum. The minimum detectable per pass fractional absorption is 1 ppm. We observe a frequency dependent ringdown cavity transmission of +/-5 ppm due to spatial variations of the mirror reflectivity. The upsilon(6) band of linear C-9 formed by laser ablation of graphite in a He molecular beam was measured, showing a factor of 2 improvement in sensitivity relative to previous IR diode laser experiments. Based on calculated IR intensities, the number density of C-9 in the molecular beam is 1.3(*)10(11) molec/cm(3) and the minimum detectable density is 1(*)10(9) molec/cm(3). We expect this spectrometer to be a powerful tool for the study of transient species formed in molecular beams. (C) 2002 American Institute of Physics.

Casaes, R. N., J. B. Paul, et al. (2004). "Infrared cavity ringdown spectroscopy of jet-cooled nucleotide base clusters and water complexes." Journal of Physical Chemistry A 108(50): 10989-10996.

We present the first direct infrared absorption measurements of gas phase nucleotide base clusters and complexes with water. Spectra in the NH stretching region indicate the presence of several doubly H-bonded isomers of both thymine and uracil dieters, as well as both larger base clusters and uracil-water complexes, but no singly H-bonded species are observed. Three NH stretching bands are assigned to three different uracil-water dieter isomers. Bands due to larger complexes are also observed, but due to spectral congestion, assignment to specific clusters is tentative. The IR cavity ringdown laser absorption spectroscopy results show unusually large bonded OH stretch red shifts for uracil-water clusters, providing evidence of the extremely strong hydrogen bonds formed between these molecules predicted in ab initio calculations.

Chapo, C. J., J. B. Paul, et al. (1998). "Is arginine zwitterionic or neutral in the gas phase? Results from IR cavity ringdown spectroscopy." Journal of the American Chemical Society 120(49): 12956-12957.

Charvat, A., S. A. Kovalenko, et al. (1999). "Attenuated total internal reflection spectroscopy with an intracavity laser absorption spectrometer." Spectrochimica Acta Part A-Molecular And Biomolecular Spectroscopy 55(7-8): 1553-1567.

A new type of intracavity laser absorption spectrometer (ICLAS) which employs an intracavity prism in total internal reflection (TIR) configuration is presented. We report a theoretical background and a full characterisation of the spectrometer by measuring absorption spectra of NO2 and I-2 vapour at room temperature in the 0.6 mu m spectral region. The ICLAS spectra measured in the attenuated TIR configuration correspond to bulk absorption with an equivalent number of reflections of 2 x 10(4). They are identical to the conventional gas phase absorption spectra with no appreciable contributions from (surface) adsorbed molecules. (C) 1999 Elsevier Science B.V. All rights reserved.

Chen, Y. Q. and L. Zhu (2001). "The wavelength dependence of the photodissociation of propionaldehyde in the 280-330 nm region." Journal Of Physical Chemistry A 105(42): 9689-9696.

We have investigated the photodecomposition of propionaldehyde (C2H5CHO; propanal) at 5 nm intervals in the 280-330 rim region by using dye laser photolysis combined with cavity ring-down spectroscopy. Absorption cross sections were determined for propionaldehyde. The HCO radical was a fragment from photodissociation. The HCO radical yields, obtained by monitoring its transient absorption at 613.8 mn, decreased with increasing C2H5CHO pressure in the 1-10 Torr range due to the increasing HCO + HCO, HCO + C2H5, and HCO + C2H5CHO reactions at higher propionaldehyde pressures and quenching by ground state propionaldehyde. After separating the contribution of HCO radical reactions, the propionaldehyde pressure quenching effect was only observed at photolysis wavelengths longer than 315 nm. Values of zero-pressure HCO yields (all lambda) and ratios of quenching to unimolecular decay rate constant of excited propionaldehyde (lambda greater than or equal to 315 nm) were given. The HCO yields (phi (HCO)degrees) were 0.98 +/- 0.06, 0.92 +/- 0.06, 0.95 +/- 0.08, 0.98 +/- 0.11, 0.91 +/- 0.05, and 1.08 +/- 0.07 at 295, 300, 305, 310, 315, and 320 rim, indicating that C2H5CHO + hv --> C2H5 + HCO is the dominant photolysis pathway. The HCO yields decreased at both the shorter-wavelength (280 nm) and the longer-wavelength (330 nm) ends. The wavelength dependence of the HCO yields from propionaldehyde photolysis was compared to that from t-pentanal ((CH3)(3)CCHO) photolysis. The HCO yields from t-pentanal photolysis decayed much more rapidly at the shorter-wavelength end, which might reveal the difference in the excited states singlet-triplet surface crossing of t-pentanal versus propionaldehyde. The dependence of the HCO yields on nitrogen buffer gas pressure was examined between 10 and 400 Torr. No dependence was observed. Cross section results were combined with HCO radical yields to estimate atmospheric photodissociation rate constants of propionaldehyde to form HCO as a function of zenith angle for cloudless conditions and at 760 Torr nitrogen pressure. Radical formation rate constants were 1.6 x 10(-5) - 4.6 x 10(-5) s(-1) for zenith angles of 0-60 degrees.

Chen, Y. Q. and L. Zhu (2003). "Wavelength-dependent photolysis of glyoxal in the 290-420 nm region." Journal Of Physical Chemistry A 107(23): 4643-4651.

We have studied the gas-phase photolysis of glyoxal, (CHO)(2), at 10 nm intervals in the 290-420 nm region by using dye laser photolysis coupled with cavity ring-down spectroscopy. Absorption cross sections of glyoxal have been measured. The HCO radical is its photodissociation product. The dependence of the HCO quantum yield on photodissociation wavelength, glyoxal pressure, and nitrogen buffer gas pressure has been determined. The HCO yields decrease with increasing glyoxal pressure in the 1-8 Torr range, owing to the increasing HCO radical reactions at higher glyoxal pressures and quenching by ground-state glyoxal. After separation of the contribution of HCO radical reactions, the aldehyde pressure quenching effect was still observed in the 320-420 nm region, and this effect increased with increasing wavelength. The HCO radical yields (all lambda) and the ratios of quenching to unimolecular decay rate constants of excited glyoxal (lambda greater than or equal to 320 nm) are given. The peak HCO yield is 2.01 +/- 0.08 (error quoted only includes la measurement uncertainty) at 390 nm, consistent with the occurrence of the (HCO)(2) + hv --> 2HCO channel. The HCO radical yields are around 1.56 +/- 0.22 in the 320-370 nm region, indicating the simultaneous occurrence of (HCO)(2) + hnu --> 2HCO and (HCO)(2) + hv --> HCO + H + CO channels. The HCO radical yields are 0.50 +/- 0.01, 0.68 +/- 0.02, and 0.84 +/- 0.07 at 290, 300, and 310 nm, respectively, which may suggest the opening of an additional photolysis channel at higher photon energies. The dependence of the HCO quantum yield on nitrogen buffer gas pressure was examined between 10 and 400 Torr. The HCO radical yields are independent of nitrogen pressure in the 290-370 nm range, but they decrease with increasing nitrogen pressure in the 380-420 nm region. A comparison of the wavelength-dependent HCO, radical yields with results obtained from previous dynamics and quenching studies provides insight into the mechanism of glyoxal photodissociation as a function of wavelength.

Chen, Y. Q., L. Zhu, et al. (2002). "Wavelength-dependent photolysis of n-butyraldehyde and i-butyraldehyde in the 280-330-nm region." Journal Of Physical Chemistry A 106(34): 7755-7763.

We have investigated the gas-phase photolysis of n-butyraldehyde (CH3(CH2)(2)CHO) and i-butyraldehyde ((CH3)(2)CHCHO) at 5 nm intervals in the 280-330 nm region using dye laser photolysis in combination with cavity ring-down spectroscopy. Absorption cross sections of both aldehydes have been measured. The quantum yields of radical/molecular photolysis products have been determined as functions of photodissociation wavelength (A), aldehyde pressure, and nitrogen buffer-gas pressure. The HCO radical is a photodecomposition product of both aldehydes. The HCO quantum yields, determined by monitoring HCO absorption at 613.8 nm, decrease with increasing aldehyde pressure in the 1-10 Torr range because of the increasing HCO + HCO, HCO + R, and HCO + RCHO reactions (R = n-C3H7 and i-C3H7) at higher aldehyde pressures and because of quenching by ground-state aldehydes. After separation of the contribution of HCO radical reactions, the aldehyde pressure quenching effect was observed only at lambda greater than or equal to 310 nm. The HCO quantum yields (at all lambda values) and the ratios of quenching to unimolecular decay rate constants of excited aldehydes (lambda greater than or equal to 310 nm) are,given. The HCO quantum yields from n-butyraldehyde photolysis are 0.52 +/- 0.05, 0.74 +/- 0.08, 0.84 +/- 0.04, and 0.77 +/- 0.08 at 305, 310, 315, and 320 nm, respectively, where the uncertainty (1sigma) represents experimental scatter only. The corresponding HCO quantum yields from i-butyraldehyde photolysis are 0.92 +/- 0.08, 1.06 +/- 0.07, 1.06 +/- 0.13, and 1.10 +/- 0.10. The differences in the peak HCO quantum yields are attributed to the opening up of the Norrish II channel (formation of C2H4 + CH3CHO) from n-butyraldehyde photolysis. The dependence of the HCO quantum yield on the nitrogen buffer-gas pressure was examined between 8 and 400 Torr; no dependence was observed. The end products from the photolysis of both aldehydes were analyzed by mass spectrometry. The occurrence of the Norrish II channel is confirmed for n-butyraldehyde.

Cheskis, S. (1999). "Quantitative measurements of absolute concentrations of intermediate species in flames." Progress In Energy And Combustion Science 25(3): 233-252.

Absolute concentration measurements of atoms and radicals in flames are very important for a better understanding of combustion mechanisms. Recently, several laser based methods were successfully used for such measurements. Among them are laser induced fluorescence (LIF), intracavity laser absorption spectroscopy (ICLAS) and cavity ring-down spectroscopy (CRDS). This article attempts to review and discuss the current status of the application of these techniques to the absolute concentration measurements in flames. The principles of two absorption spectroscopy methods, ICLAS and CRDS, are discussed in more detail as these methods are only at the beginning stage of their application to combustion diagnostics. The final portion of the review is devoted to discussing some recent measurements of absolute concentrations of radicals in hydrocarbon flat premixed flames and comparing these measurements with computer simulations. (C) 1999 Elsevier Science Ltd. All rights reserved.

Cheskis, S., I. Derzy, et al. (1998). "Cavity ring-down spectroscopy of OH radicals in low pressure flame." Applied Physics B-Lasers And Optics 66(3): 377-381.

Cavity ring-down laser spectroscopy (CRDS) is used to measure the OH concentration profile and the rotational temperature profile in low-pressure (30 torr) methane/air flames. Very high sensitivity (2 x 10(10) molecules/cm(3)) and large dynamic range (more than 20000) are demonstrated. CRDS also provides accurate temperature measurements, with statistical errors less than 2%. Measured concentration profiles are in reasonable agreement with calculated values. It is observed that in the preflame zone (where the temperature is about 1000 K), the OH concentration at the first vibrational excited state is about seven times larger than the equilibrium OH(v "-1) concentration at this temperature.

Choi, Y., J. Park, et al. (2004). "Kinetics and mechanism of the C6H5+CH3CHO reaction: Experimental measurement and theoretical prediction of the reactivity towards four molecular sites." Chemphyschem 5(5): 661-668.

The kinetics and mechanism of the reaction of C6H5 with CH3CHO have been investigated experimentally and theoretically. The total rate constant for the reaction has been measured by means of the cavity ring-down spectrometry (CRDS) in the temperature range 299-501 K at pressures covering 20-75 Torr. The overall bimolecular rate constant can be represented by the expression k=(2.8+/-0.2)x10(11) exp[-(700+/-30)/T] cm(3)mol(-1)s(-1), which is slightly faster than for the analogous C6H5 + CH2O reaction determined with the same method in the some temperature range. The reaction mechanism for the C6H5+CH3CHO reaction was also explored with quantum -chemical calculations at various hybrid density functional theories (CFTs) and using ob initio high-level composite methods. The theories predict that the reaction may occur by two hydrogen-abstraction and two addition channels with the aldehydic hydrogen-abstraction reaction being dominant. The rate constant calculated by the transition state theory for the aldehydic hydrogen-abstraction reaction is in good agreement with the experimental result after a very small adjustment of the predicted reaction barrier (+0.3 kcal mol(-1)). Contributions from other product channels are negligible under our experimental conditions. For combustion applications, we have calculated the rate constants for key product channels in the temperature range of 298-2500 K under atmospheric-pressure conditions; they can be represented by the following expressions in units of cm(3) mol(-1)s(-1): k(1,cho)=8.8 x 10(3)T(2.6) exp(-90/T), k(2,ch3) = 6.0 x 10(1)T(3.3) exp(-950/T), k(3a)(C6H5COCH3 + H) = 4.2 x 10(5)T(0.6) exp(-410/T) and k(3b)(C6H5CHO + CH3) = 6.6 x 10(9)T(-0.5) exp (-310/T).

Choi, Y. M. and M. C. Lin (2004). "Kinetics and mechanisms for the reactions of phenyl radical with ketene and its deuterated isotopomer: An experimental and theoretical study." Chemphyschem 5(2): 225-232.

Kinetics and wmechanism for the reaction of phenyl radical (C6H5) with ketene (H2Cbeta=C-alpha=O) were studied by the cavity ring-down spectrometric (CRDS) technique and hybrid DFT and ab initio molecular orbital calculations. The C6H5 transition at 504.8 nm was used to detect the consumption of the phenyl radical in the reaction. The absolute overall rate constants measured, including those for the reaction with CD2CO, can be expressed by the Arrhenius equation k = (5.9 +/- 1.8) x 10(11) exp[-(1160 +/- 100)/T] cm(3) mol(-2) s(-1) over a temperature range of 301-474 K. <LF>The absence of a kinetic isotope effect suggests that direct hydrogen abstraction forming benzene and ketenyl radical is kinetically less favorable in good agreement with the results of quantum chemical calculations at the G2MS//B3LYP6-31G(d) level of theory for all accessible product channels, including the above abstraction and additions to the C-alpha, C-beta, and O sites. For application to combustion, the rate constants were extrapolated over the temperature range of 298-2500 K under atmospheric pressure by using the predicted transition-state parameters and adjusted entrance reaction barriers E-alpha, E-beta - 1.2 kcal mol(-1); they can be represented by the following expression in units of cm(3) mol(-1) s(-1) k(alpha) -6.2 x 10(19) T-2.3 exp[= 7590/T] and kbeta - 3.2 x 10(4) T-2.4 exp[-246/T].

Choi, Y. M., J. Park, et al. (2003). "Experimental and computational studies of the kinetics and mechanisms for C6H5 reactions with acetone-h(6) and -d(6)." Journal Of Physical Chemistry A 107(39): 7755-7761.

Kinetics and mechanisms for the C6H5 + CH3C(O)CH3 and CD3C(O)CD3 reactions have been investigated by cavity ring-down spectrometry (CRDS) and hybrid density functional theory (DFT) calculations. The rate constants measured for the two reactions at the constant pressure of 45 Torr using Ar as a carrier gas can be represented by the following Arrhenius expressions in units of cm(3) mol(-1) s(-1): k(H) = (4.2 +/- 0.4) x 10(11) exp[-(955 +/- 30)/T] and k(D) = (5.1 +/- 0.6) x 10(11) exp[-(1114 +/- 43)/T] in the temperature ranges of 299-451 and 328-455 K, respectively. The significant kinetic isotope effect observed suggests that H-abstraction is the major path, according to their activation energies, with the C6H5 + CD3C(O)CD3 reaction being higher by 0.3 kcal/mol. DFT calculations at the B3LYP/aug-cc-PVTZ//B3LYP/cc-PVDZ level of theory indicate the reaction can in principle take place by three reaction paths, one H-abstraction and two addition reactions to the C=O double bond at both C and 0 atom sites, with the latter two processes having significantly higher reaction barriers. The rate constants predicted by canonical variational transition state theory (CVT) with small curvature tunneling (SCT) corrections for the direct H- and D-abstraction reactions are in reasonable agreement with the experimental data after slightly decreasing the calculated barriers from 3.9 kcal/mol to 3.3 kcal/mol and from 4.7 kcal/mol to 4.1 kcal/mol, respectively. The predicted rate constants for C6H5 + CH3COCH3 in the temperature range of 298-1200 K can be represented reasonably by the expression, kH (1.7 +/- 0.6) x 10(-1) T ((4.2 +/- 0.1)) exp[-(466 +/- 26)/T] cm(3) mol(-1) s(-1).

Choi, Y. M., J. Park, et al. (2004). "Formation and decomposition of phenylvinylperoxy radicals in the reaction: C6H5C2H2+O-2." Chemphyschem 5(8): 1231-1234.

Cias, P., M. Araki, et al. (2004). "Gas phase detection of cyclic B-3: 2(2)E(')<- X(2)A(1)(') electronic origin band." Journal Of Chemical Physics 121(14): 6776-6778.

The rotationally resolved origin band in the 2 E-2(')<--X (2)A(1)(') electronic spectrum of cyclic B-3 has been observed by cavity ring down spectroscopy in the gas phase. The B-3 molecule was generated in a supersonic planar plasma containing decaborane (B10H14) and neon as a carrier gas. The rotational structure pattern is that of a cyclic molecule. It is analyzed assuming an equilateral triangle in both electronic states. The band origin is determined to be 21 853.52 cm(-1), and the bond lengths 1.603 77(106) Angstrom in the ground and 1.619 07(96) Angstrom in the excited electronic state are inferred from analysis of the rotational structure. (C) 2004 American Institute of Physics.

Cias, P., O. Vaizert, et al. (2002). "Electronic gas-phase spectrum of the pentaacetylene cation." Journal Of Physical Chemistry A 106(42): 9890-9892.

The origin band of the A(2)Pi(u) - X(2)Pi(g) electronic transition of the linear pentaacetelyne cation, HC10H+, and isotopic derivatives, HC10D+ and DC10D+, has been recorded in the gas phase. The absorption spectrum was observed by cavity ring down spectroscopy through a supersonic planar plasma expansion. The spectrum comprises both spin-orbit components with resolved P- and R-branches. Contour fits allow the determination of ground and excited state spectroscopic constants.

Clemitshaw, K. C. (2004). "A review of instrumentation and measurement techniques for ground-based and airborne field studies of gas-phase tropospheric chemistry." Critical Reviews In Environmental Science And Technology 34(1): 1-108.

The development, applications and intercomparisons of instrumentation and measurement techniques for ground-based and airborne field studies of gas-phase tropospheric chemistry are reviewed. Filter radiometry, chemical actinometry and scanning spectroradiometry for j-NO2 and j-((OD)-D-1) are described. Detection of OH using L-POAS/DOAS, MOAS, LIF/FAGE and CIMS is discussed. Observations of NO3 using DOAS, MIESR and CRDS, and of HO2 and RO2 With CA, CIMS/IMR-MS, MIESR, and LIF/FAGE are also reviewed. GC-FID, GGECD and GC-MS analyses of NMHCs and alkyl, peroxyacyl and bi-functional organic nitrates are described, together with applications of CIMS/PTR-MS, DOAS and LIE CO measurements utilising GFC, GC-HgO/UV, VUV-RF and TDLAS are presented. Measurements Of O-3 using UV photometry, chemiluminescence, electro-chemistry, LIDAR/DIAL and DOAS are discussed. Chemiluminescence and LIF detection methods for NO with photochemical and thermal convertors for NO2 and NOy are also discussed, as are TDLAS, MIESR, DOAS, CRDS and other approaches for NO2. HONO measurements using DOAS, CIMS, CRDS, TDLAS, denuder systems, chemiluminescence and on-line analyses of NO2- are described. For HONO2, filter packs, denuder systems, chemiluminescence methods, mist chambers, TDLAS, CIMS and LIF are presented. Direct and indirect fluorimetric, chromatographic and spectroscopic detection techniques are discussed for CH2O and higher carbonyls. Observations of H2O2 and ROOH utilising colorimetry, chemiluminescence, fluorescence, HPLC and TDLAS are also described.

Cormier, J. G., R. Ciurylo, et al. (2002). "Cavity ringdown spectroscopy measurements of the infrared water vapor continuum." Journal Of Chemical Physics 116(3): 1030-1034.

We report measurements of the water vapor continuum using infrared cavity ringdown spectroscopy at frequencies of 931.002, 944.195, and 969.104 cm(-1). Our values of the water vapor continuum coefficients for self-broadening at T=296 K are C-s(0) (931 cm(-1))=2.23 +/-0.17, C-s(0)(944 cm(-1))=2.02 +/-0.13, and C-s(0)(969 cm(-1))=1.79 +/-0.21x10(-22) molecules(-1) cm(2) atm(-1). Our measurements are found to be in good agreement with the far wing line shape theory of Ma and Tipping, but we find that empirical models of the water vapor continuum, widely used in radiative transfer calculations, significantly overestimate the observed self-broadened continuum. (C) 2002 American Institute of Physics.

Corner, L., H. R. Barry, et al. (2003). "Comparison of cross-section measurements of the 2 nu(5) overtone band of formaldehyde determined by cavity ringdown and cavity enhanced spectroscopy." Chemical Physics Letters 374(1-2): 28-32.

We have measured the integrated cross-section of a transition at 5676.08 cm(-1) in the 2v(5) overtone band of formaldehyde to be (3.09 +/- 0.10) x 10(-23) cm(2) cm(-1) by cavity ringdown spectroscopy using a tunable diode laser. This measurement was used to calculate the integrated cross-section of the R-Q(1)(10) line at 5676.21 cm(-1) as (5.8 +/- 0.5) X 10(-22) cm(2) cm(-1). We compare this figure to our value of this cross-section measured using the technique of cavity enhanced absorption spectroscopy of (5.7 +/- 0.6) x 10(-22) cm(2) cm(-1) and find the results to be in good agreement. (C) 2003 Elsevier Science B.V. All rights reserved.

Crawford, T. M. (1985). "Error Sources In The Ring Down Optical Cavity Decay Time Mirror Reflectometer." Proceedings Of The Society Of Photo-Optical Instrumentation Engineers 540: 295-302.

Cronin, T. J. and L. Zhu (1998). "Dye laser photolysis of n-pentanal from 280 to 330 nm." Journal Of Physical Chemistry A 102(50): 10274-10279.

The UV photolysis of n-pentanal in the 280-330-nm region has been studied in 5-nm intervals by using dye laser photolysis in combination with cavity ring-down spectroscopy. Absorption cross sections of n-pentanal were measured at each wavelength studied. n-Pentanal exhibited a broad, structureless absorption band similar, in appearance, to that of previously studied short-chain aldehydes. The absorption spectrum peaked at 295 nm with a cross section of (6.56 +/- 0.17) x 10(-20) cm(2) molecule(-1). The formation of the HCO radical, which is a photodissociation product, was monitored in these experiments. The HCO yield was found to be independent of n-pentanal pressure (2-18 Torr) and total pressure (8-480 Torr) except for 325- and 330-nm photolysis where the size of the HCO signal was small and the dissociation was near the threshold. The dependence of the HCO radical yield on the photolysis wavelength was determined. The HCO yields were 0.058 +/- 0.006, 0.095 +/- 0.009, 0.10 +/- 0.02, 0.14 +/- 0.01, 0.10 +/- 0.02, 0.15 +/- 0.02, 0.14 +/- 0.02, 0.20 +/- 0.06, 0.14 +/- 0.02, 0.085 +/- 0.034, 0.087 +/- 0.015 at 280, 285, 290, 295, 300, 305, 310, 315, 320, 325, and 330 nm, respectively, where uncertainty reflects experimental scatter only. End products from closed-cell photolysis of n-pentanal with and without O-2 were investigated at 290, 310, and 330 nm by using GC/MS and HPLC. Acetaldehyde was found to be a significant product from the photodissociation of n-pentanal/N-2 mixtures. Photolysis rates of n-pentanal to form HCO were calculated for two representative atmospheric conditions (noontime at sea level and 40 degrees N latitude on January 1 and on July 1). The estimated radical formation rate constants from n-pentanal photolysis were about twice as fast as those obtained from acetaldehyde photolysis.

Crosson, E. R., P. Haar, et al. (1999). "Pulse-stacked cavity ring-down spectroscopy." Review Of Scientific Instruments 70(1): 4-10.

Pulse stacking, or synchronous pumping, is a novel approach that offers important advantages in cavity ring-down spectroscopy. Using an ultrashort pulse, high repetition rate laser source we have shown that it is possible to resonantly stack pulses in a high finesse cavity, significantly enhancing the decay wave forms obtained when the laser source is abruptly terminated. We have achieved signal-to-noise ratio improvements of several orders of magnitude compared to single pulse injection systems, demonstrating a sensitivity of 2 x 10(-9) cm(-1) at 5.38 mu m. (C) 1999 American Institute of Physics. [S0034-6748(99)04801-7].

Crosson, E. R., K. N. Ricci, et al. (2002). "Stable isotope ratios using cavity ring-down spectroscopy: Determination of C-13/C-12 for carbon dioxide in human breath." Analytical Chemistry 74(9): 2003-2007.

We have constructed a cavity ring-down spectrometer employing a near-IR external cavity diode laser capable of measuring C-13/C-12 isotopic ratios in CO2 in human breath. The system, which has a demonstrated minimum detectable absorption loss of 3.2 x 10(-11) cm(-1) Hz(-1/2), determines the isotopic ratio of (COO)-C-13-O-16-O-16/(COO)-C-12-O-16-O-16 by measuring the intensities of rotationally resolved absorption features of each species. As in isotope ratio mass spectrometry (IRMS), the isotopic ratio of a sample is compared to that of a standard CO2 sample calibrated to the Pee Dee Belemnite scale and reported as the sample's delta(13)C value. Measurements of eight replicate CO2 samples standardized by IRMS and consisting of 5% CO2 in N-2 at atmospheric pressure demonstrated a precision of 0.22parts per thousand for the technique. delta(13)C values were also obtained for breath samples from individuals testing positive and negative for the presence of Helicobacter pylori, the leading cause of peptic ulcers in humans. This study demonstrates the ability of the instrument to obtain delta(13)C values in breath samples with sufficient precision to serve as a useful medical diagnostic.

Czyzewski, A., S. Chudzynski, et al. (2001). "Cavity ring-down spectrography." Optics Communications 191(3-6): 271-275.

We propose a modified cavity ring-down spectroscopy (CRDS) technique. A pulsed broad band laser is applied as a light source while a spectrograph equipped with gated ICCD camera is used for the signal detection. The signal is simultaneously analyzed at various wavelengths within the laser line width. It allows to get the information on absorption spectra much faster and more reliable than by means of classical CRDS method with tunable laser. (C) 2001 Published by Elsevier Science B.V.

Czyzewski, A., K. Ernst, et al. (2002). "Investigation of kinetics of CH-radicals decay by cavity ring-down spectroscopy." Chemical Physics Letters 357(5-6): 477-482.

We describe application of cavity ring-down spectroscopy (CRDS) for monitoring of CH-radicals produced by pulsed electric discharge in methane. The method provides opportunity to follow changes of concentration of the reaction product within a few microseconds. (C) 2002 Published by Elsevier Science B.V.

Czyzewski, A., K. Ernst, et al. (2002). "Cavity ring-down spectroscopy for trace gas analysis." Acta Physica Polonica B 33(8): 2255-2265.

Cavity Ring-Down Spectroscopy (CRDS) is a novel technique of measurement of the absorption coefficient based on determination of the Q-factor of an optical resonator which contains the investigated absorber. We present a modified CRDS method (so called CRD-Spectrography) in which the signal is simultaneously analysed within a broad spectral range. This technique was used for monitoring of trace gases (nitrogen oxides) in the atmosphere. Another modification of CRDS technique allows to determine the transient absorption coefficient. This method was applied for studies of kinetics of CH radical produced by pulsed electric discharge in methane.

Dahnke, H., D. Kleine, et al. (2001). "Real-time monitoring of ethane in human breath using mid-infrared cavity leak-out spectroscopy." Applied Physics B-Lasers And Optics 72(8): 971-975.

We report on spectroscopic real-time analysis of ethane traces in exhaled human breath. Ethane is considered the most important volatile marker of free-radical induced lipid peroxidation and cell damage in the human body. Our measurements were carried out by means of mid-infrared cavity leak-out spectroscopy in the 3 mum region, a cw variant of cavity ring-down spectroscopy. The spectrometer is based on a CO overtone laser with tunable microwave sidebands. The resulting system proved to be an unique tool with high sensitivity and selectivity for rapid and precise breath testing. With a 5 s integration time, we achieved a detection limit on the order of 100 parts per trillion ethane in human breath. Thus, sample preconcentration is unnecessary. Time-resolved monitoring of the decaying ethane fraction in breath after smoking a cigarette is demonstrated.

Dahnke, H., D. Kleine, et al. (2001). "Isotopic ratio measurement of methane in ambient air using mid-infrared cavity leak-out spectroscopy." Applied Physics B-Lasers And Optics 72(1): 121-125.

We report on infrared laser spectroscopic measurements of the isotopic composition of methane ((CH4)-C-12, (CH4)-C-13) in natural air samples with a cavity ring-down technique. A CO overtone sideband laser is utilized to excite a high-finesse cavity which provides an effective optical absorption path length of 3.6 km. We achieved a detection limit of 105 ppt methane in ambient air using an integration time of 20 s. This corresponds to a minimum detectable absorption of 1.9 x 10(-9) /cm. Rapid determination of the C-13/C-12 isotopic ratio of methane in ambient air without sample preconcentration or gas processing is realized. The present system requires only few minutes for an isotopic ratio measurement with a precision of 11 parts per thousand.

Dahnke, H., G. Von Basum, et al. (2002). "Rapid formaldehyde monitoring in ambient air by means of mid-infrared cavity leak-out spectroscopy." Applied Physics B-Lasers And Optics 75(2-3): 311-316.

We report the spectroscopic detection of formaldehyde in ambient air using cavity leak-out spectroscopy, a cw variant of cavity ring-down spectroscopy. This technique proved to be suitable for a real-time quantitative analysis of polluted air without any preprocessing of the air sample. Using a tunable CO-overtone sideband laser for the; = 3 mum spectral region and a ring-down cell with R = 99.95% mirrors, we achieved a detection limit of 2 parts per billion formaldehyde in ambient air, corresponding to a minimum detectable absorption coefficient of 7 x 10(-9)/cm (sampling time: 2 s). Calibration problems arising from the polarity of the molecule and due to HITRAN database uncertainties are discussed.

DeMille, S., R. H. deLaat, et al. (2002). "Comparison of CRDS to ICL-PAS and phase-shift CRDS spectroscopies for the absolute intensities of C-H (Delta upsilon(CH)=6) overtone absorptions." Chemical Physics Letters 366(3-4): 383-389.

Cavity ring-down spectroscopy (CRDS) has been used to obtain the visible overtone spectra (Deltanu(CH) = 6) of neopentane, C(CH3)(4), propane, C3H8, and n-butane, C4H10, yielding absolute f-values for the transitions to better than 3%. For the neo-pentane overtone intensity, comparison with a recent measurement using intra-cavity laser photoacoustic spectroscopy (ICL-PAS) provides favourable agreement, with improved precision. Being absolute this value may be used as a standard for relative intensity measurements obtained by ICL-PAS. The measured propane and n-butane overtone intensities, when compared to recent work using phase-shift CRDS, indicate a lack of agreement to quoted uncertainties. (C) 2002 Elsevier Science B.V. All rights reserved.

Denisov, A., T. W. Schmidt, et al. (2004). "Sulfur terminated nanowires in the gas phase: laser spectroscopy and mass spectrometry." International Journal Of Mass Spectrometry 233(1-3): 131-136.

The products of a CS-hydrocarbon discharge are elucidated through a combination of mass spectrometry and laser spectroscopy. Sulfur containing species are identified and their structures proposed using spectroscopic considerations. The resonant 2-color 2-photon ionization A(2) Pi <-- X(2)Pi spectrum of HC6S is presented, confirming previous non-mass selective identification. The origin band of the A(2) Pi <--X-2 Pi transitions of HCSS and HC10S were measured at 14838.4(l) and 13333.7(5) cm(-1) by cavity ringdown spectroscopy. The near linear relationship of absorption wavelength and chain length characterizes these species as molecular nanowires exhibiting cumulenic bonding. From these data HC12S is estimated to absorb at 820 +/- 5 nm. (C) 2004 Elsevier B.V. All rights reserved.

Derzy, I., V. A. Lozovsky, et al. (1999). "Absolute CH concentration in flames measured by cavity ring-down spectroscopy." Chemical Physics Letters 306(5-6): 319-324.

Cavity ring-down spectroscopy (CRDS) was used to measure absolute concentration profiles of the CH radical in low-pressure methane/air flames. The Q(1)(4) rotational line of the C(2)Sigma(+) <-- (XII)-I-2 band at 315 nm was used for concentration measurements. Very high sensitivity (2 X 10(10) cm(-3)) is demonstrated. The measured profiles are in good agreement with that calculated using the GRI-Mech mechanism. (C) 1999 Elsevier Science B.V. All rights reserved.

Derzy, I., V. A. Lozovsky, et al. (1999). "CH, NH, and NH2 concentration profiles in methane/air flames doped with N2O." Israel Journal Of Chemistry 39(1): 49-54.

Intracavity Laser Absorption Spectroscopy (ICLAS) and Cavity Ring Down Spectroscopy (CRDS) were used to measure concentration profiles of the CH, NH, and NH2 radicals in a low-pressure (30 Torr) stoichiometric methane/oxygen/ nitrogen flat flame doped with a small amount of nitrous oxide (1.7%). Concentration profiles of the CH and NH radicals were measured by CRDS, whereas the NH2 radical profile was measured by ICLAS. Temperature profiles were obtained using measured CRDS spectra of the OH radical. The radical absorption spectra were recorded with good signal-to-noise ratio. For the first time, absolute concentrations of NH and NH2 were measured in flames of this kind, The obtained experimental profiles and peak amounts agree well with model predictions based on GRI-Mech 2.11 (Gas Research Institute Mechanism). The mechanism also describes well the observed decreasing CH concentration with addition of N2O.

Derzy, I., V. A. Lozovsky, et al. (2000). "Absorption spectroscopy measurements of NH and NH2 absolute concentrations in methane/air flames doped with N2O." Proceedings Of The Combustion Institute 28: 1741-1748.

Intracavity laser absorption spectroscopy ICLAS) and cavity ring-down spectroscopy (CRDS) were used to measure concentration profiles of NH2 and NH in low-pressure (30 torr) methane/oxygen/nitrogen flames doped with a small amount of N2O. High sensitivity of these absorption spectroscopy methods uas demonstrated (4 x 10(10) cm(-3) for NH and 8 x 10(10) cm(-3) for NH2). The absolute NH concentrations agree well with those predicted by the GRI-Mech 2.11 mechanism and one-dimensional PREMIX code. The absolute NH2 concentrations in the lean flame are fitted well by the calculations, but in the stoichiometric and the rich flames, the observed concentrations are about twice that predicted. In the rich flame (phi = 1.2), the calculations underpredict the NH concentrations at large distances from the burner. The strongest difference was found for the NH2 radical at large distances above the burner The strong spectra of NH2 were observed even at 40 mm above the burner where the model calculations predict very; insignificant concentration of NH2. The observed discrepancy can be caused by limitations of both the chemical mechanism and one-dimensional PREMIX code used for calculations.

Ding, H. B., A. J. Orr-Ewing, et al. (1999). "Rotational structure in the (A)over-tilde(1)A ''-(X)over-tilde(1)A ' spectrum of formyl chloride." Physical Chemistry Chemical Physics 1(18): 4181-4185.

High-resolution cavity ring-down spectroscopy has been used to record three vibronic bands of the (A) over tilde(1)A"(1)-(X) over tilde(1)A' (pi*<--n(O)) transition of room-temperature formyl chloride (HClCO). These three bands (6(0)(1), 5(0)(1)6(0)(1) and 2(0)(1)5(0)(1)6(0)(1)) are all vibronically induced through the activity of the out-of-plane inversion vibration nu(6), and are found to obey type-a selection rules. Rotational constants have been derived from the analysis of these bands and used to give information on the geometrical structure of the excited state. The properties of the (A) over tilde are found to be intermediate between those of the corresponding states of formaldehyde and formyl fluoride.

Ding, Y., P. Macko, et al. (2004). "High sensitivity cw-cavity ringdown and Fourier transform absorption spectroscopies of (CO2)-C-13." Journal of Molecular Spectroscopy 226(2): 146-160.

The absorption spectrum of (CO2)-C-13 has been recorded by cw-cavity ringdown spectroscopy with a new set up based on fibered DFB lasers. By using a series of 31 DFB lasers, the spectrum of carbon dioxide could be recorded in the 6130-6750 cm(-1) region with a typical sensitivity of 5 x 10(-10) cm(-1). The spectrum has also been recorded between 4400 and 8500 cm(-1) with a Fourier transform spectrometer associated with a multi-pass cell (maximum path length of 105 in). The new observations obtained both by FTS and CRDS represent a significant extension of the available data. For instance, more than 4000 line positions were measured and assigned in the CRDS spectrum while only 232 line positions are listed in the HITRAN database. Altogether, the band by band analysis has led to the determination of the rovibrational parameters of 65, 7, and 24 bands for the (CO2)-C-13-O-16, (OCO)-O-16-C-13-O-17, and (OCO)-O-16-C-13-O-18 isotopomers, respectively. As some observed line positions show significant deviations from the predictions of the effective Hamiltonian model, the new observed line positions were gathered with the data available in the literature to refine the set of effective Hamiltonian parameters of the (CO2)-C-13-O-16 isotopic species. The refined set of 96 effective Hamiltonian parameters reproduces more than 14 650 line positions of (CO2)-C-13-O-16 with an RMS = 0.002 cm(-1). A detailed comparison with the line positions retrieved from Venus spectra and the line list provided by HITRAN is also presented and discussed. (C) 2004 Elsevier Inc. All rights reserved.

Dreyer, C. B., S. M. Spuler, et al. (2001). "Calibration of laser induced fluorescence of the OH radical by cavity ringdown spectroscopy in premixed atmospheric pressure flames." Combustion Science And Technology 171: 163-190.

Cavity ringdown spectroscopy (CRDS) of the hydroxyl radical (OH) has been explored in a laminar methane-air flame at atmospheric pressure over a range of equivalence ratio. Laser-induced fluorescence (LIF) of OH calibrated by CRDS in a lean flame compares well to PREMIX calculations using GRI-Mech 3.0. CRDS is a highly sensitive path-integrated diagnostic technique that can yield absolute absorber number densities via a relatively small number of measurable parameters. Among the chief advantages of CRIDS is that the measurement is independent of laser power and that the same laser used for LIF can be used for CRIDS with only a simple insertion of optics and detector for CRIDS. Since LIF has a large dynamic range and high spatial resolution, it is the preferred OH diagnostic for flame studies, however, it is difficult to directly quantify LIF measurements. For this reason, quantitative OH LIF measurements are normally obtained by calibration of the LIF signal using an independent technique. The utility of quantitative OH CRDS measurements for calibration of LIF in these flames is shown.

Drucker, S., J. L. Van Zanten, et al. (2004). "Triplet excited states probed by cavity ringdown spectroscopy." Journal Of Molecular Structure 692(1-3): 1-16.

Despite their photochemical importance, molecular triplet states have received relatively little attention in spectroscopic studies. This is primarily due to the challenge of detecting the spin-forbidden T-n <-- S-0 transitions. To meet the challenge, we have implemented cavity ringdown (CRD) spectroscopy, a high-sensitivity absorption technique, in our studies of photochemically relevant triplet species. In this article we outline the sensitivity requirements for observing singlet-triplet transitions and show how CRD detection achieves the needed sensitivity. We also specify the construction and operating details we used to set up the CRD spectroscopy system in our laboratory. Finally, we review investigations from our laboratory and others that have exploited the sensitivity of CRD detection to obtain triplet data that was not previously available. These studies include measurement of vibronically resolved T-n <-- S-0 spectra of some cyclic enones and conjugated hydrocarbons. (C) 2004 Elsevier B.V. All rights reserved.

Duan, H. L., G. A. Zaharias, et al. (2002). "Detecting reactive species in hot wire chemical vapor deposition." Current Opinion In Solid State & Materials Science 6(5): 471-477.

Major recent advances: A variety of in situ diagnostic techniques have been applied recently to detect reactive species, including H, Si, SiH, SiH2, SiH3, and Si2H6, in hot wire chemical vapor deposition of hydrogenated silicon films. Several recent studies confirmed silicon radicals as a. major silane decomposition product from the hot wire. The dependence of silicon production on filament temperature measured in the different studies appears to be similar; however, the reported apparent activation energies vary across research groups. (C) 2002 Elsevier Science Ltd. All rights reserved.

Duan, Y. X., C. J. Wang, et al. (2003). "Exploration of microwave plasma source cavity ring-down spectroscopy for elemental measurements." Analytical Chemistry 75(9): 2105-2111.

We are exploring sensitive techniques for elemental measurements using cavity ring-down spectroscopy (CRDS) combined with a compact microwave plasma source as an atomic absorption cell. The research work marries the high sensitivity of CRDS with a low-power microwave plasma source to develop a new instrument that yields high sensitivity and capability for elemental measurements. CRDS can provide orders of magnitude improvement in sensitivity over conventional absorption techniques. Additional benefit is gained from a compact microwave plasma source that possesses the advantages of low power and low-plasma gas flow rate, which are of benefit for atomic absorption measurements. A laboratory CRDS system consisting of a tunable dye laser is used in this work for developing a scientific base and demonstrating the feasibility of the technique. A laboratory-designed and -built sampling system for solution sample introduction is used for testing. The ring-down signals are monitored using a photomultiplier tube and recorded using a digital oscilloscope interfaced to a computer. Lead is chosen as a typical element for the system optimization and characterization. The effects of baseline noise from the plasma source are reported. A detection limit of 0.8 ppb (10(-10)) is obtained with such a device.

Dudek, J. B., P. B. Tarsa, et al. (2003). "Trace moisture detection using continuous-wave cavity ring-down spectroscopy." Analytical Chemistry 75(17): 4599-4605.

We have developed an instrument to measure trace concentrations of small hydride species in gases using continuous-wave cavity ring-down spectroscopy with near-infrared diode laser excitation. An rms baseline equivalent absorbance of 9.2 x 10(-11) cm(-1)/rootn is found, where n is the number of ring-down transients. When the 1396.376-nm absorption line of water is used, this corresponds to a noise equivalent moisture concentration in nitrogen gas of 68 pptv/rootn. Water vapor concentration is detected over a range extending from 3 to 1000 ppbv and found to depend linearly on the concentration as determined by a calibrated commercial moisture sensor.

Dupre, P. (2001). "Probing molecular species by cavity ringdown laser absorption spectroscopy, application to the spectroscopy and dynamics of jet-cooled NO2." Comptes Rendus De L Academie Des Sciences Serie Iv Physique Astrophysique 2(7): 929-964.

The Cavity Ringdown Laser Absorption Spectroscopy (CRLAS or CRDS) technique has acquired a enviable audience in the spectroscopy community during the past decade. Based on a high-Q optical cavity, it largely bypasses the advantages of multipass absorption cells, offering ppm range sensitivities or better, and emulates rapid developments of the experimental configurations. The basic idea consists of measuring the intracavity electromagnetic field time behavior which reflects the cavity optical properties and medium losses. This article is divided in three main parts. The first one is devoted to the description of the CRLAS technique, including: (i) a brief formalism about the principles of an empty high-Q cavity (Fabry-Perot) coupled to an incoming electromagnetic field and (ii) the absorption model allowing one to deal with absorbing species inserted inside the cavity. The second part succinctly reviews and compares some of the usual highly sensitive spectroscopy techniques and the main applications of the CRLAS technique are presented. The last part of the paper reports the recent results obtained at the laboratory concerning the NO2 molecular species excited by a CW single mode laser source and under slit jet expansion conditions. Two energy ranges are primarily investigated, firstly the region around 800 nm in which three kinds of behaviors are identified Doppler-limited linear absorption. Doppler-free two-photon absorption and saturation absorption. Secondly. by using radiation at 397 nm, the lowest photodissociation threshold of NO2 is interrogated in order to address the unimolecular reaction processes. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.

Emig, M., R. I. Billmers, et al. (2002). "Sensitive and selective detection of paramagnetic species using cavity enhanced magneto-optic rotation." Applied Spectroscopy 56(7): 863-868.

Cavity enhanced magneto-optic rotation spectroscopy (CEMOR) is a technique that utilizes a high-finesse cavity within a traditional magnetic rotation experimental setup to realize the benefits of both cavity ringdown and magneto-optic methods simultaneously. By observing Ga atoms at their resonance line of 417.204 nm, we demonstrate that CEMOR allows selective detection of paramagnetic species with lower detection limits than can be obtained through either flame atomic absorption or magnetic rotation spectroscopies. Quantitative CEMOR measurements of Ga in an air-acetylene flame reveal a 101 sensitivity increase over conventional flame atomic absorption in our experimental setup. Sample concentration is shown to impact the temporal behavior of transmitted signals, resulting in a significant time shift in transmission of peak signal intensity. Such time shifting has not been theoretically predicted, and we report its first experimental demonstration. The work discussed herein suggests that the CEMOR technique can be used to simplify the study of species such as combustion-generated radicals, which often absorb weakly and occur in spectral regions crowded by stronger molecular absorption lines.

Enami, S., Y. Nakano, et al. (2004). "Reactions of Cl atoms with dimethyl sulfide: A theoretical calculation and an experimental study with cavity ring-down spectroscopy." Journal Of Physical Chemistry A 108(39): 7785-7789.

The adduct formation in the reactions of Cl and Br atom with dimethyl sulfide (DMS) is studied theoretically and experimentally. The rate constants of the forward reaction at several temperatures and pressures are determined from the rise and decay time profiles of the adduct, Cl-DMS, using cavity ring-down laser spectroscopy. The high-pressure limit rate constant for the Cl-DMS adduct formation is determined to be k(1a)(high) = (2.2 +/- 0.2) X 10(-10) cm(3) molecule(-1) s(-1). The rate constant of Cl with DMS at atmospheric pressure is k(1) = (3.6 +/- 0.2) x 10(-11) cm(3) molecule(-1) s(-1). Error bars are 1sigma. The Arrhenius plot of the forward reaction has a negative temperature dependence for 278-318 K. The calculated equilibrium constants of the reaction Cl and Br with DMS at 300 K are K-CIDMS = 2.8 x 10(-12) and K-BrDMS = 7.7 x 10(-15) cm(3) molecule(-1), respectively. The binding energy (D-0) is calculated to be 17.7 kcal mol(-1) for Cl-DMS, and 14.1 kcal mol(-1) for Br-DMS. D-0(Br-C) is in fair agreement with the previously reported experimental value, 12 +/- 1 kcal mol(-1). The results are discussed in comparison with previous experimental reports of the bromine atom adduct, Br-DMS. Atmospheric implications regarding the fate of the X-DMS adducts (X = Cl and Br) in the troposphere are discussed.

Enami, S., J. Ueda, et al. (2004). "Formation of iodine monoxide radical from the reaction of CH2I with O-2." Journal Of Physical Chemistry A 108(30): 6347-6350.

The rate constants of 10 radical formation from the reaction of CH2I with O-2 were determined in the pressure range of 5-80 Torr with N-2 diluent at 278-313 K, using cavity ring-down spectroscopy. The room temperature rate constant is (4.0 +/- 0.4) x 10(-13) cm(3) molecule(-1)s(-1) at 30 Torr total pressure. No significant dependences on temperature and total pressure were observed. The yield of 10 from CH2I + O-2 was estimated to be unity in 100 Torr total pressure of N-2 diluent.

Enami, S., J. Ueda, et al. (2004). "Temperature-dependent absorption cross sections of ozone in the Wulf-Chappuis band at 759-768 nm." Journal Of Geophysical Research-Atmospheres 109(D5).

[1] Absorption cross sections of ozone in the Wulf-Chappuis band at 759-768 nm have been determined using cavity ring-down spectroscopy at 215-298 K. Precise measurements at 762.07 and 764.47 nm revealed a slight temperature dependence of the absorption cross sections: sigma(762.07 nm, 298 K) = (2.86 +/- 0.04) x 10(-22) cm(2) molecule(-1); sigma(762.07 nm, 215 K) = (2.62 +/- 0.04) x 10(-22); sigma(764.47 nm, 296 K) = (2.70 +/- 0.03) x 10(-22); and sigma(764.47 nm, 214 K) = (2.44 +/- 0.03) x 10(-22). Results at 762.07 nm are indistinguishable within the experimental uncertainties from those reported by Burkholder and Talukdar [1994]. Results from the present work facilitate a more accurate retrieval of atmospheric temperature, cloud height, and cloud coverage data from satellite measurements of absorption by O-2 in the A band around 761 nm.

Engel, G., W. B. Yan, et al. (1999). Ring-down spectroscopy with a Brewster's angle prism resonator. Laser Spectroscopy XIV International Conference. R. Blatt, J. Eschner, D. Leibfried and F. Schmidt-Kaler. Singapore, World Scientific: 314-315.

Engelking, P. C. (1991). "Spectroscopy Of Jet-Cooled Ions And Radicals." Chemical Reviews 91(3): 399-414.

Engeln, R., G. Berden, et al. (1998). "Cavity enhanced absorption and cavity enhanced magnetic rotation spectroscopy." Review Of Scientific Instruments 69(11): 3763-3769.

It is experimentally demonstrated that a narrow band continuous wave (cw) light source can be used in combination with a high-finesse optically stable cavity to perform sensitive, high-resolution direct absorption and optical rotation spectroscopy in an amazingly simple experimental setup, using ideas from the field of cavity ring down spectroscopy. Light from a scanning narrow band cw laser is coupled into the cavity via accidental coincidences of the laser frequency with the frequency of one of the multitude of modes of the cavity. The absorption and polarization rotation information is extracted from a measurement of the time-integrated light intensity leaking out of the cavity as a function of laser wavelength. (C) 1998 American Institute of Physics. [S0034-6748(98)01811-5].

Engeln, R., G. Berden, et al. (1997). "Polarization dependent cavity ring down spectroscopy." Journal Of Chemical Physics 107(12): 4458-4467.

We here theoretically outline and experimentally demonstrate that polarization spectroscopy can be combined with cavity ring down (CRD) spectroscopy, thereby retaining the specific advantages of both techniques. The b(1) Sigma(g)(+)(v'= 2) <-- X-3 Sigma(g)(-)(v'' = 0) transition of molecular oxygen around 628 nm is used to demonstrate the possibility to selectively measure either the polarization-dependent absorption or the resonant magneto-optical rotation of gas-phase molecules in the appropriate setup. Just as in CRD absorption spectroscopy, where the rate of absorption is measured, in the here presented polarization-dependent CRD (PDCRD) detection scheme the rate of polarization rotation is measured, which enables the polarization rotation to be quantitatively determined. Apart from studying electro-optic and magneto-optic phenomena on gas-phase species, the PDCRD detection scheme is demonstrated to be applicable to the study of magneto-optical rotation in transparent solid samples as well. (C) 1997 American Institute of Physics.

Engeln, R., K. G. Y. Letourneur, et al. (1999). "Detection of CH in an expanding argon/acetylene plasma using cavity ring down absorption spectroscopy." Chemical Physics Letters 310(5-6): 405-410.

Cavity ring down (CRD) absorption spectroscopy is used to measure the methylidyne (CH) radical in an Ar/C2H2 plasma. The rotational spectrum of the A(2)Delta(nu' = 0) <-- (XII)-I-2(nu "= 0) transition around 430 nm is recorded to determine the total CH ground state density, both as a function of the current through the are producing the low-pressure Ar plasma and as a function of the injected acetylene flow. Total ground state densities between 5 X 10(15) and 8 X 10(16) m(-3) are detected. The trends show that the methylidyne radical plays a minor role in the growing mechanism of hydrogenated amorphous carbon films and is predominantly formed in the charge exchange/dissociative recombination channel starting from the C2H radical. (C) 1999 Elsevier Science B.V. All rights reserved.

Engeln, R. and G. Meijer (1996). "A Fourier transform cavity ring down spectrometer." Review Of Scientific Instruments 67(8): 2708-2713.

We present a pulsed multiplex absorption spectrometer in which the sensitivity of the cavity ring down absorption detection technique is combined with the multiplex advantage of a Fourier Transform spectrometer. A description of the Fourier transform cavity ring down (CRD) spectrometer-substantiated with first experimental results on the atmospheric band of molecular oxygen-is given. It is shown that as in the case of normal CRD spectroscopy, the measurement is independent of light intensity fluctuations provided the spectral intensity distribution of the light source is known and is constant during the measurement. (C) 1996 American Institute of Physics.

Engeln, R., E. vandenBerg, et al. (1997). "Cavity ring down spectroscopy with a free-electron laser." Chemical Physics Letters 269(3-4): 293-297.

A cavity ring down (CRD) absorption experiment is performed with a free-electron laser (FEL) operating in the 10-11 mu m region. A short infrared pulse of approximately 20 ns, sliced from the much longer FEL pulse, is used to measure CRD spectra of ethylene in two different ways. First, ''ordinary'' CRD spectra with a resolution determined by the bandwidth of the FEL (approximate to 5 cm(-1)) are recorded, Second, Fourier transform (FT) CRD spectra with a resolution that is in principle determined by the FT-spectrometer are obtained by analyzing the light exiting the ring down cavity with a FT-spectrometer while the FEL is operated in broadband mode. (C) 1997 Elsevier Science B.V.

Engeln, R., G. von Helden, et al. (1999). "Cavity ring down spectroscopy on solid C-60." Journal Of Chemical Physics 110(5): 2732-2733.

Engeln, R., G. vonHelden, et al. (1996). "Phase shift cavity ring down absorption spectroscopy." Chemical Physics Letters 262(1-2): 105-109.

Cavity ring down absorption spectroscopy with a continuous light source is used to measure the transition frequencies and absolute absorption coefficient of the weak b(1) Sigma(g)(+) (v' = 2) <-- X(3) Sigma(g)(-) (v '' = 0) transition of O-18(2). The absorption spectrum is extracted from a measurement of the magnitude of the phase shift that an intensity modulated continuous light beam experiences upon passing through an unstabilized optical cavity.

Evers, F., J. Giraud-Girard, et al. (2001). "Absorption and fluorescence excitation spectra of 9-(N-carbazolyl)-anthracene: Effects of intramolecular vibrational redistribution and diabatic transitions involving electron transfer." Journal Of Physical Chemistry A 105(12): 2911-2924.

The absorption and fluorescence excitation spectra of 9-(N-carbazolyl)-anthracene (C9A) in vibronically excited S-1 states are measured and calculated by means of a simple model. Accordingly, C9A is excited from torsional states \0(j)] of the electronic ground-state So to diabatic torsional states \1l] of the bright electronically excited state S-1, which are coupled to states \2l] of the dark electronically excited-state S-2. In addition, all torsional states are coupled to the other vibrations of C9A. The model parameters are adapted from bur previous papers yielding good agreement of the experimental and theoretical fluorescence emission spectrum and fluorescence lifetimes of C9A. The present additional agreement for the experimental and theoretical absorption and fluorescence excitation spectra confirms the simple model, which implies rather weak couplings of the torsional bright state S-1 but strong coupling of the dark state S-2 to the other vibrations of C9A, respectively. This points to different electronic structures of these excited states. This conjecture is confirmed by quantum chemical calculations based on density functional theory (DFT) that reveal the covalent structure of S-1, in contrast with the TICT (twisted intramolecular charge transfer) behavior of S-2.

Evertsen, R., A. Staicu, et al. (2002). "Pulsed cavity ring-down spectroscopy of NO and NO2 in the exhaust of a diesel engine." Applied Physics B-Lasers And Optics 74(4-5): 465-468.

The application of pulsed cavity ring-down spectroscopy has been demonstrated for the in situ quantitative determination of NO and NO2 in the exhaust of a diesel engine. NO absorption has been monitored at the transition from the X(2)Pi ground state to the A(2)Sigma(+) state at 226 nm. For NO2, absorption bands in the spectral region from 438 nm to 450 nm were used. At the selected engine conditions, concentrations of 212 +/- 22 ppm and 29 +/- 4 ppm have been measured for NO and NO2, respectively, in good agreement with separate chemical exhaust gas analysis. The method is sensitive enough to meet the European Euro V standard directive on NOx emissions. This communication discusses the relatively simple setup needed for this type of measurement, the problems encountered, as well as the prospects for single-stroke, simultaneous measurements of both NO and NO2 at the sub-ppm level.

Evertsen, R., R. L. Stolk, et al. (1999). "Investigations of Cavity Ring Down Spectroscopy applied to the detection of CH in atmospheric flames." Combustion Science And Technology 149(1-6): 19-34.

The application of Cavity Ring Down Spectroscopy for the quantitative determination of CH densities in atmospheric flames has been investigated. Two different atmospheric flames have been studied: a premixed burner stabilised flat CH4/air flame and an oxyacetylene flame from a welding torch, which is used for diamond deposition. For the methane flame density profiles of CH are obtained and compared with densities calculated by De Goey and Van Oijen (1998). The temperature is derived from the measured Boltzmann distribution. The data from the oxyacetylene flame are compared to LIF profiles measured by Klein-Douwel et al. (1995).

Evertsen, R., R. L. Stolk, et al. (2000). "Investigations of cavity ring down spectroscopy applied to the detection of CH in atmospheric flames (vol 157, pg 341, 2000)." Combustion Science And Technology 157: 341-342.

Evertsen, R., J. A. Van Oijen, et al. (2003). "Measurements of absolute concentrations of CH in a premixed atmospheric flat flame by cavity ring-down spectroscopy." Combustion And Flame 132(1-2): 34-42.

Absolute concentrations of CH in a premixed, atmospheric flat flame of CH, and air have been det