Rotational relaxation matrix for fast non-Markovian collisions

The present paper is focused on the development of an adequate description of collisionally induced dephasing and rotational energy transfer (RET) in the CO 2 Fermi dyad n 1 /2n 2 . We have made comparative analysis of two approaches to RET simulation for the 2n 2 Q-branch 1285 cm −1 based on spectral exchange (SE) and rotational relaxation (RR) ideas. A special fitting procedure based on the minimization of an approximation error has been developed for fitting theoretical impulse responses to the experimental ones measured by picosecond time-domain coherent anti-Stokes Raman spectroscopy (CARS). A series of experiments on frequency-domain CARS were carried out in order to improve measurements of the dephasing time T 2 and to extend the simulation to the whole gas density range using a uniform set of fitting parameters. Special attention was paid to a detailed analysis of the rotational structure manifestation in the impulse response beating structure. In the case of the 'red' Q-branch, the RR model proved to be more appropriate in comparison with the SE model. It is shown that the rotational structure contribution to the time-domain signal decay and the cumulative spectral width remains essential and comparable with the collisional dephasing contribution up to the highest gas densities.

Section: Introductionsupporting

confidence: 59%

Collisionally induced dephasing and rotational energy transfer in the CO₂ Fermi dyad ‘red’ Q‐branch 1285 cm⁻¹

Arakcheev

Киреев

Morozov

et al. 2007

“…The fixed values of the -matrix parameters were obtained by scaling the values known for nitrogen. 18 For simplicity, it was also assumed that these parameters remain equal for the ground and upper states. The net rotational rates found for the upper  state agree satisfactorily with those derived from LIF measurements.…”

Section: Theorymentioning

confidence: 99%

State‐resolved collisional energy transfer of OH, NH and H₂CO by two‐color resonant four‐wave mixing spectroscopy

Radi

Kouzov

2002

Extra resonances observed in two-color resonant four-wave mixing (TC-RFWM) spectra, which originate from collision-induced energy transfer processes, were investigated experimentally and theoretically. It is shown that the resonances yield information on state-to-state rotational energy transfer (RET) occurring in the ground and excited states of OH and NH. The measurements were performed in situ in an equilibrium medium of high temperature and high density. The results shed more light on the propensity rules for the change in the fine-structure label and rotational quantum number of NH. A comparison with a recent investigation of NH RET on the ground-state potential yielded good agreement. A theoretical frequency-domain picture was developed with the help of exact (off-diagonal) relaxation matrices and general four-level schemes. The theoretical results were compared with measured relative TC-RFWM intensities of the OH radical obtained in a flame. Furthermore, the investigation on diatomic radicals was extended to the polyatomic formaldehyde (H 2 CO) molecule. Initial cell experiments were performed at low pressure by using CO 2 as a quencher. The observation of collision-induced resonances in the ground state of H 2 CO indicate the potential of the method for the investigation of RET processes occurring in polyatomic molecules in equilibrium media.

“…The development of such an approach became possible only recently. 3 Based on a non-Markovian extension of the energycorrected sudden (ECS) approximation, 4 the novel approach goes beyond standard ECS, the latter being commonly used to interpret only the core of spectra where the impact (Markovian) approximation is valid. The non-Markovian approach of Ref.…”

Section: Introductionmentioning

confidence: 99%

“…The non-Markovian approach of Ref. 3 has thus far been successfully applied, by Bonami and Buldreyreva, to the interpretation of the rototranslational spectra of nitrogen, at various densities, and their temperature dependence. 5,6 Here, the fact that the carbon dioxide molecule, although polyatomic, is linear in its 1 mode encouraged us to attempt a description of its anisotropic spectrum with the formalism of Refs 5 and 6. ion laser whose beam was polarized perpendicular to the scattering plane (the plane formed by the incident beam and the direction in which the scattered light is detected).…”

Section: Introductionmentioning

confidence: 99%

On far‐wing Raman profiles by CO₂

Benec'h

Rachet

Chrysos

et al. 2002

The anisotropic scattering spectrum of the symmetric stretching n 1 band by CO 2 was recorded up to the far Stokes wing, and its theoretical analysis was attempted through the non-Markovian energy-corrected sudden approximation -a useful approach which has thus far been successfully applied to the anisotropic scattering spectrum by N 2 , up to the far wing. Despite the excellent agreement observed in N 2 here, a substantial inconsistency between theory and experiment was found in the wing of the spectrum. Although the influence of other missing processes or neighboring bands cannot be totally excluded, our findings rather suggest that highly anisotropic perturbers, such as CO 2 , are improperly described when they are handled as point-like molecules, a cornerstone hypothesis in the approach employed.