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Infrared chemiluminescence from vibrationally excited CO and from vibrationally excited HCl was observed when C2H3Cl, 1,1-C2H2Cl2, cis- and trans-1,2-C2H2Cl2, or C2HCl3was introduced into a stream of oxygen atoms. The mechanisms describing the reactions of oxygen atoms with these molecules are discussed in detail. The initial step is postulated to involve the formation of an aldehyde and a carbene. The reaction step responsible for the formation of CO†is postulated to beand for HCl†

The noise level in single-pulse resonant nitrogen CARS spectra is shown to decrease with increasing pump laser bandwidth. This is the reverse of the trend observed for nonresonant CARS spectra. The precision of single-pulse CARS temperature measurements is shown to be dramatically increased by performing a weighted fit of theoretical and experimental CARS spectra using the measured detector noise coefficients as weighting parameters. The inclusion of collisional narrowing and cross-coherence in the CARS theory calculations and their effect on best fit temperatures are discussed. These temperatures, measured in a flat-flame burner, are compared with those obtained by Na line-reversal.

Spectrally resolved measurements of noise in resonant nitrogen coherent anti-Stokes Raman spectroscopy (CARS) are presented for three pump laser bandwidths. The experimental noise curves are compared with those calculated from a simple model involving statistically independent Stokes modes. The sources of noise in both resonant and nonresonant CARS spectra are discussed.

A broadband CARS system designed to measure flame temperature from hot nitrogen CARS spectra is described, and a source of temperature error is identified and attributed to nonlinear behavior of the optical multichannel diode array detector. Detector sensitivity, linearity, uniformity, and noise are discussed. Data are presented for the Tracor-Northern TN-1223-4GI and TN-6132 detectors. It is shown that the nonlinearity observed with CARS signals is a function of radiation density at the detector input plane. This nonlinearity is associated with saturation in the microchannel plate intensifier and should be observable with short duration high intensity light pulses other than CARS, and with intensified detectors (both diode array and vidicon) other than the Tracor-Northern. The nonlinearity observed with the TN-1223-4GI detector can be eliminated by reducing the radiation density. At maximum sensitivity the detector shot noise contributes a significant component to the shot-to-shot variation of the spectral profile of the CARS signal.

An investigation of single pulse coherent anti-Stokes Raman spectroscopy (CARS) noise, determined by the analysis of broadband nonresonant spectra, is described. It is shown that the use of a single-mode rather than a multimode pump laser leads to a significant reduction of CARS noise (40%), down to the level exhibited by the Stokes spectral profile itself. This reduction in noise is attributed to the minimization of the effects due to random variations in the laser temporal profiles by using temporally smooth single-mode laser pumps. A measurement of detector shot noise is presented and its effect on CARS noise is described. The advantages of using a single-mode pump laser in CARS spectroscopy are discussed.

Chemiluminescence attributable to the Swan, Phillips, and Ballik–Ramsay bands of C2was observed when halomethanes of the form CH2−nX2+n(X = Cl, Br, I) were introduced into a stream of hydrogen atoms. The relative population of the ν′ = 0 levels of the A3Πg, b1Πuand A′ 3∑g−states are 10:400:1000 with the total rate of formation into all three states being approximately equal. The principal step for the formation of C2* is believed to be

Spatial averaging is a potential problem in the application of coherent anti-Stokes Raman spectroscopy (CARS) to combustion diagnostics when varying temperatures and composition are present at spatial scales smaller than the typical 1–2-mm spatial resolution of CARS. The observed CARS spectrum is then a mixture of the hot and cold components. We show that simulated, spatially averaged spectra, generated by the incoherent addition of intensities, can be significantly different from those obtained by the coherent addition of the electric field amplitudes of the component spectra. The analyses of these simulated, spatially averaged CARS spectra demonstrate that the use of theoretical CARS spectra, generated by the addition of intensities of the hot and cold components of a binary gas mixture, can lead to errors in the estimated flame temperatures.

The noise in single-shot coherent anti-Stokes Raman (CARS) spectroscopy that employs a broadband modeless dye laser (MDL) is examined and the results are compared with those of a conventional dye laser. The noise of the dye-laser, the nonresonant CARS, and the resonant N_2 CARS signals are determined. The use of a MDL is shown to result in substantially reduced CARS noise when the CARS signal is generated with a single-mode pump laser, but only a marginal reduction of noise is observed with a multimode pump source The noise measurements are compared with theoretical predictions that are based on models that assume modes of random amplitudes and phases in the multimode laser sources. The combination of a MDL and a single-mode pump laser is shown to increase the precision of single-shot N_2 CARS temperature measurements.

The total nonresonant susceptibilities of C_3H_8, CO_2, and C_2H_4, measured by fitting the coherent anti-Stokes Raman spectra of binary mixtures of these gases and nitrogen with theoretical N_2 CARS spectra are reported. These measurements are compared with the values in the literature obtained by CARS and other techniques. For propane and carbon dioxide, the effect of including their contribution to the broadening of nitrogen Raman lines on the inferred nonresonant susceptibilities is also examined.

The image persistence of self-scanning photodiode arrays (IPDA) incorporating P-20 phosphor-based intensifies is shown to make them unsuitable for single-pulse CARS temperature measurements in turbulent combustion. Correcting CARS flame spectra for the nonlinear response of the IPDA detectors increases CARS derived temperatures ≈3–6%. This error is partially offset by correcting for the perturbations in the N_2 vibrational population resulting from stimulated Raman pumping. The effect of these population perturbations on CARS-derived temperatures is determined. CARS flame spectra obtained with uncorrected pump beams that are corrected for IPDA nonlinearity and stimulated Raman pumping are shown to give temperatures in good agreement with combined thermocouple/sodium line-reversal measurements.

Several self-scanning photodiode arrays (IPDA) used for CARS spectroscopy are shown to exhibit a greater image persistence than has generally been realized, and to exhibit a falloff in sensitivity that is logarithmic with decreasing output signal. These effects are attributed to the P-20 phosphor based intensifiers used in the IPDAs and are probably generic to all such detectors. A strategy for minimizing the image persistence in CARS spectroscopy is presented. A prototype detector incorporating a much faster rare earth phosphor is evaluated and shown to be more suited to single pulse CARS measurements in turbulent combustion than the IPDAs incorporating P-20 phosphors.

The decomposition of gas mixtures containing ozone has been studied following a short duration u.v. light pulse. From an analysis of the O3decomposition curves for O3:N2and O3:H2O mixtures, it is shown that the relative rate of O(1D) reaction with H2O and N2is It is also shown that less than6% of the O2, formed directly by photolysis, is in the state. The water catalyzed decomposition of ozone is also discussed.

Infrared chemiluminescence from vibrationally excited CO was observed when CH3Cl, CH2Cl2, CHCl3, or CH2Br2was introduced into a stream of oxygen atoms. Emission from vibrationally excited HCl was also observed from CH2Cl2and CHCl3. The mechanisms describing the reactions of oxygen atoms with these molecules are discussed in detail. The reaction step responsible for the formation of CO† is postulated to beand for HCl†

The decomposition of ozone has been studied following a short duration u.v. light pulse. From an analysis of the O3decomposition curves for O3:N2, O3:N2:O2and O3:O2mixtures it is shown that the relative rate constant for O(1D) deactivation by N2and O2is given by It is also shown that O2(1Σg+) is formed in at least 75% of the collisions in which O(1D) is deactivated by O2. The rate constants of the reactions O2(1Σg+) + O3 → 2O2+O and O + O2 + O2 → O3 + O2are found to be (2.3 ± 0.5) × 10−11 cm3molecule−1s−1and (5.0 ± 0.5) × 10−34 cm6molecule−2s−1, respectively, at (295 ± 1) °K.

The thermal decompositions of tetramethyltetrazene (TMT) and tetraethyltetrazene (TET) have been studied using a flow system. It is shown that both the decompositions occur at, or above, the limiting pressure for unimolecularity, and Arrhenius parameters for both decompositions are obtained. The decomposition mechanism is discussed in relation to the Arrhenius parameters and theories of three-fragment decompositions. Preliminary values of some kinetic parameters for some reactions of dialkylamino radicals are presented.