Rotation–vibration CARS spectra of the 2ν2 mode in CO2 gas

Polarized and depolarized CARS band shapes are reported for the 2ν2 band of the Fermi resonance diad in room temperature CO2 gas at a series of densities. Analysis of the spectra yields vibrational relaxation times and the shift of the band center with density. Comparison of the depolarized spectra with the J diffusion model for reorientation shows that there is good agreement. Effective collision frequencies are obtained for various densities. The frequency shifts, the inverse vibrational relaxation time and the collision frequency are all linear functions of density except at the highest densities. Binary collision cross sections are calculated for angular momentum and for vibrational relaxation. The advantages of these and other CARS measurements relative to more conventional spectroscopies are briefly discussed.