Theory of vibrational line width in dense gases

Abstract

The quantum theory of j-diffusion has been employed to calculate the isotropic Raman Q-branch width in dense gases. The contributions of the Q-branch width have been estimated from two competitive mechanisms: dephasing of the molecular vibration and rotational energy relaxation. Owing to the long-range dipole-dipole interaction the contribution from the resonance V-V transfer to the dephasing relaxation rate may prove to be prevailing. The Q-branch width has been discussed as a function of the density of perturbing particles, temperature and interaction potential parameters. The theoretical results are in good agreement with the experimental data obtained from Raman spectra of N 2, CO and N 2O in the gas phase.