One-photon laser excitation of Xe(6s[3/2]2) and Kr(5s[3/2]2) atoms that were generated in a discharge-flow reactor was used to study the collisional relaxation of the Kr(5p′[3/2]1, [3/2]2, and [1/2]1), the Xe(7p[3/2]2, [3/2]1, [5/2]2, and [5/2]3), and the Xe(6p′[3/2]1, [3/2]2, and [1/2]1) states in He and Ar. Both cw and pulsed laser excitation techniques were utilized to obtain the total deactivation rate constants and product formation rate constants at 300 K. Collisions with He mainly produce Xe* and Kr* product states with small energy defects, but the rate constants can be as large as 20×10−10 cm3 atom−1 s−1, which correspond to thermally averaged cross sections of 150 Å2. Because of the rapid collisional coupling of populations in nearly isoenergetic levels, multicomponent exponential decay of the initially produced state is frequently observed. The deactivation rate constants for Ar are smaller than for He, but the product distributions tend to be more diverse than for He, and arguments based only on energy defects are not necessarily a good guide to the favored product state(s) from Ar collisions. The magnitude of the quenching cross sections for Ar is consistent with the crossing of an entrance channel with several diabatic exit channel potentials. However, the superlarge quenching cross sections for Xe*–He to just one or two product levels require special considerations. The Kr(5p′) and Xe(6p′ and 7p) rate constants with He are discussed with respect to collisional effects upon the use of cw optical pumping to convert populations in the metastable Xe(6s[3/2]2) and Kr(5s[3/2]2) levels to the Xe(6s′[1/2]0) and Kr([5s′[1/2]0) levels.

A compact, pulsed Nd:YAG laser-based instrument has been built to measure in situ absolute gas temperatures in large industrial furnaces by use of spontaneous anti-Stokes Raman scattering. The backscattering configuration was used to simplify the optics alignment and increase signal-to-noise ratios. Gated signal detection significantly reduced the background emission that is found in combustion environments. The anti-Stokes instead of the Stokes component was used to eliminate contributions to spectra from cold atmospheric nitrogen. The system was evaluated in a methane/air flame and in a bench-top oven, and the technique was found to be a reliable tool for nonintrusive absolute temperature measurements with relatively clean gas streams. A water-cooled insertion probe was integrated with the Raman system for measurement of the temperature profiles inside an industrial furnace. Gas temperatures near 1500-1800 K at atmospheric pressure in an industrial furnace were inferred by fitting calculated profiles to experimental spectra with a standard deviation of less than 1% for averaging times of approximately 200 s. The temperatures inferred from Raman spectra are in good agreement with data recorded with a thermocouple probe.

The spectroscopic and kinetic consequences associated with the strong homogeneous interactions between (i) CO(b 3Σ+,v′=0) and CO(a′ 3Σ+, v′=30, 31, and 32), (ii) CO(b 3Σ+,v′=1) and CO(a′ 3Σ+, v′=34, 35, and 36), (iii) CO(b 3Σ+,v′=2) and CO(a′ 3Σ+, v′=40 and 41) levels are evaluated. Mixing of b 3Σ+ character into the a′ 3Σ+ levels reduces the radiative lifetimes of the latter, because the lifetimes of pure b 3Σ+ and a′ 3Σ+ states are approximately 50 ns and 3 μs, respectively. The strength of the interaction changes with rotational level, and the rotational line intensities and the radiative branching to different v″ levels of the CO(a′ 3Σ+–a 3Π) transition are strongly affected. Comparison of high resolution CO(a′, v′=31, 34, and 35) experimental spectra with calculated spectra shows a marked underestimation of the rotational temperature of these CO(a′,v′) levels unless the mixing is explicitly recognized. With benefit of this knowledge, some results from the Kr(5s′[1/2]0)+CO excitation-transfer reaction need to be reinterpreted. Emission spectra for 300 K rotational distributions from CO(b,v′=0, 1, and 2) and CO(a′,v′=30, 31, 34, and 35) were used to obtain vibrational band intensities for comparison with model calculations. Analysis of the pressure and time dependence of the laser-induced fluorescence data permit the electronic relaxation mechanism of the CO(b,v′=0, 1, 2) and CO(a′,v′=31 and 35) levels in He buffer gas to be discussed. The experimental radiative lifetimes of CO(b,v′=0,1,2) were measured as 60±6, 63±4, and 58±4 ns, respectively. The role of the homogeneously perturbed levels in the collisional relaxation mechanism is discussed.

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