STUDY OF COLLISIONAL EFFECTS ON BAND SHAPES OF THE NU-1/2-NU-2 FERMI DYAD IN CO2 GAS WITH STIMULATED RAMAN-SPECTROSCOPY .1. ROTATIONAL AND VIBRATIONAL-RELAXATION IN THE 2-NU-2 BAND

The 2ν2 component of the Fermi dyad ν1/ 2ν2 of CO2 has been studied with high-resolution stimulated Raman spectroscopy (SRS). The behavior of the band shape has been explored in a large density range: 0.2 to 50 amagat at a temperature of 295 K and 0.5 to 20 amagat at 500 K. Energy corrected sudden (ECS) and modified energy gap (MEG) laws are used to model the relaxation matrix in order to account for the collisional narrowing induced by rotational energy transfers. ECS model allows us to accurately determine the vibrational shift and width as a function of density by fitting the experimental spectra, leading to the determination of the vibrational relaxation coefficients for the 2ν2 mode. Connection is established between the present calculations of the collisionally narrowed SRS spectra based on the diagonalization of the relaxation matrix, which applies for any line overlap, and the usual spectral line shape for weak line coupling. Particular emphasis is put on the situation of strong collapse and on the concomitant predominance of the vibrational dephasing. © 1990 American Institute of Physics.