Vibrational energy relaxation of polyatomic solutes in simple liquids and supercritical fluids

A microscopic statistical mechanical theory of vibrational energy relaxatio n rates for polyatomic solutes in simple solvents is presented. The theory is based on a model of a spherical solute present at infinite dilution in a fluid of spherical solvent particles, and the solute-solvent interaction p otential depends on the vibrational coordinates of the solute. The theory i s applied to study the experimentally observed anomalous density and temper ature dependence of vibrational relaxation rates in supercritical fluids in the vicinity of the critical point. A quantitative comparison of the theor y with experiment is presented, and the agreement is satisfactory. (C) 2000 American Institute of Physics. [S0021-9606(99)51347-0].