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

Abstract

AbstractThe present paper is focused on the development of an adequate description of collisionally induced dephasing and rotational energy transfer (RET) in the CO2 Fermi dyad ν1/2ν2. We have made comparative analysis of two approaches to RET simulation for the 2ν2 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 T2 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. Copyright © 2007 John Wiley & Sons, Ltd.