Generalized Brownian dynamics. III. Vibrational relaxation of heteronuclear diatomics in rare gases

A simple, classical stochastic model has been developed to study the vibrational energy relaxation of heteronuclear diatomic molecules in simple monatomic liquids. This work is an extension of an earlier study on homonuclear diatomic molecules [D. E. Smith and C. B. Harris, J. Chem. Phys. 92, 1312 (1990)]. The model is based on the generalized Langevin equation for generalized Brownian dynamics. The memory function of each atom in the diatomic is determined directly from classical molecular dynamics simulations in the solvent of interest and then scaled by a screening factor. The memory function is modeled using an autoregressive technique, which provides efficient evaluation of the friction integral. The effect of screening is accounted using a simple model based on the equilibrium structure of the diatomic in the Lennard-Jones solvent, which is shown to provide very reasonable results. The model developed is applied to simulate the vibrational relaxation of iodine chloride, ICl, in its ground electronic state in liquid xenon. Good agreement is found between the stochastic and molecular dynamics simulations. This is encouraging considering the fact that the stochastic technique is computationally more efficient and has been generalized from homonuclear to heteronuclear diatomics. It also indicates that the underlying assumptions, such as the linear response approximation, are valid in the present stochastic model