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

Abstract

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.

Effects of O2–CO2 polarization beating on femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy of O2

“…This behavior can be explained by considering the rotational line spacing of O 2 and CO 2 molecules. The CO 2 rotational line spacing in both Fermi dyads is <0.01 cm −1 [23,24], whereas the average rotational line spacing of the O 2 ν = 0 ← ν = 1 band is ∼1 cm −1 [18]. At the time of the initial impulsive excitation, the various ro-vibrational Raman coherences of each molecule begin to oscillate in phase but become slightly out of phase as a result of the very small frequency differences between the rotational transitions.…”

“…In fs-CARS of O 2 , while the O 2 Raman transition is excited at 1556 cm −1 , Fermi dyads of CO 2 at 1285 cm −1 and 1388 cm −1 will be simultaneously excited because of the broad bandwidths of the pump and Stokes lasers [23][24][25]. The simultaneous excitation of O 2 and CO 2 Raman transitions is illustrated schematically in Fig.…”

“…In this temperature range the presence of 10% CO 2 does not cause any noticeable change in the coherence dephasing rates and, hence, is unlikely to cause deviations in the temperature extracted using the O 2 fs-CARS model. This is particularly advantageous since the spectroscopy of a triatomic molecule such as CO 2 can be significantly more complicated than that of diatomic molecules [23,24].…”

Collisionally induced dephasing and rotational energy transfer in the CO2 Fermi dyad ‘blue’ Q‐branch 1388 cm−1

“…The RR model proved to be more appropriate for the 'red' Q-branch. 32 In the present paper, we compare the application of both approaches to the 'blue' ( 1 ) Q-branch. In order to improve the measurements of the dephasing time T 2 and to extend the modeling to a broader range, we also carried out a series of experiments on frequency-domain CARS in which the 1388 cm 1 Q-branch spectral width was measured in the complete gas density region.…”

ECONOS in the epoch of CARS renaissance

“…Two contributions from Arakcheev et al 19,20 deal with a collisionally induced dephasing and rotational energy transfer in the CO 2 Fermi dyad. The first paper 19 develops a model for the description of collisionally induced dephasing and rotational energy transfer in the 1285 cm 1 (red) Q-branch of the CO 2 Fermi dyad.…”