A memory–functions approach to vibrational relaxation in dense media

Abstract

We propose a new method to study some effects concerned with vibrational relaxation in dense molecular media. Our approach makes use of the memory-functions technique to result in a clear physical description of the behavior in the system. The crucial point in this study is the introduction of a noninteracting reference system with regard to which the perturbation parameters in the real system are derived. These parameters consist of a time-modulation parameter τ and an interaction parameter labeled κ2 which accounts for the real-system spectral fourth moment. We show how the last parameter may be obtained from spectral measurements on the system. The time parameter which describes (by means of a Poisson distribution) a stochastic process for the random force acting on the molecules remains as an adjustable parameter. We compare our results with some existing simplified calculations and note the possibility of estimating the range of τ from such calculations. We apply our method to some new experimental data on AsH3 to obtain very good agreement between theory and experiment.