Vibrational and rotational collisional relaxation in CO2–Ar and CO2–He mixtures studied by stimulated Raman-infrared double resonance

Abstract

The collisional relaxation among vibrational levels of the Fermi dyad of CO2 mixed with Ar and He (10% CO2, 90% rare gas) has been studied at room temperature with a double resonance experiment. Stimulated Raman effect from the ground state achieved the pumping process with a Nd:YAG laser and a pulse amplified dye laser. After pumping the v1 or 2v2(Σ+g) level, a cw CO2 laser was used to probe either the depopulation rates of the pumped levels (vibrationally or rotationally resolved) or the energy transfer rates to neighboring states. The vibrational energy relaxation has been studied from experimental depopulation of v1 and population of 2v2 levels through a five-level model. A full set of vibrational rates has been determined and compared with other experimental and theoretical works when available. Our measurements could stimulate new accurate calculations. The rotational energy transfer among the J-resolved rotational levels of 2v2 has been observed for J=14 to 34 with a maximum difference between pumped and probed levels of ΔJ=20. The numerous experimental data have been modeled through a relaxation model based on the energy corrected sudden (ECS) approximation. The adjustable parameters of the ECS matrix have been directly determined by fitting the experimental time-dependent population curves. The diagonal elements of this matrix agree well with experimental linewidths. The resulting ECS relaxation matrix can be used to calculate line shapes in high-pressure coherent Raman spectra of v1 and 2v2 bands or infrared absorption spectra. In contrast, the inelastic linewidths of 2v2 deduced from depopulation data are in disagreement with available experimental linewidths, as already shown in numerous previous studies of gases and mixtures.

Activated Dissociation of CO2 on Rh(111) and CO Oxidation Dynamics

“…It is plausible that gas-phase translational to rotational or rotational to rotational collisional energy transfer may have influenced the apparent rotational temperature of the desorbing CO 2 . − The chemiluminescence experimentalists 17 conservatively estimate that 65% of the CO 2 molecules detected had at most a single gas-phase collision with the CO supersonic molecular beam flux of 6.7 × 10 18 molecules per cm 2 per second impinging on the surface or with the ambient O 2 gas. Although it would be reassuring if lower pressure CO oxidation measurements could be performed to eliminate any ambiguity about possible rotational cooling or heating of the CO 2 product, the finding of a product rotational temperature fairly close to the surface temperature for an activated surface reaction is not uncommon.…”

Line-space description of resonant four-wave mixing: Theory for isotropic molecular states

“…TheŴ-matrix is also a key quantity to exhaustively interpret the picosecond laser-induced fluorescence (LIF) responses 10 and those a) Electronic mail: alex@ak1197.spb.edu obtained by coherent anti-Stokes Raman techniques, both in time [11][12][13][14][15] and frequency [16][17][18] domains. The vibrational band shapes measured by Raman gain/loss techniques 19,20 should also be acknowledged as sensible tools for checking theŴmatrix models.…”

Inverse R aman Spectrometry

“…72 This work was generalized to study collisional relaxation in CO 2 -Ar and CO 2 -He mixtures. 73 The CARS technique was used to study the line-mixing effect in a   type hot band, taking into account the vibration-rotation angular momentum coupling. 74 …”

“…107 The SRS technique was used to detect a hole burned in the rotational distribution of the ground state when a CW CO 2 laser was tuned to the n 3 band. This experiment can be considered a precedent for other double resonance techniques such as Raman-IR 73 and Raman-Raman. 87 Very recently, the SRS spectrum of this molecule has been recorded in the n 2 region.…”