A THEORY OF VIBRATIONAL-ENERGY RELAXATION IN LIQUIDS

A microscopic statistical mechanical theory of the vibrational energy relaxation of a diatomic solute in an atomic solvent is presented. The diatomic is treated as a breathing Lennard-Jones sphere. The relaxati on rate is obtained from the Fourier transform of the force-force time -correlation function. The latter is expanded in powers of time (up to t(4)), and expressions for the expansion coefficients are derived usi ng equilibrium statistical mechanics. These coefficients are used to d etermine the parameters of an analytic ansatz for this correlation fun ction, which can be evaluated at all times (and thus can be Fourier tr ansformed). The resulting theory for the time-correlation function is compared to numerical results from a molecular dynamics simulation. Th eoretical results for the vibrational relaxation rate are compared to experiments on I-2 in Xe over a wide range of densities and temperatur es. (C) 1996 American Institute of Physics.