SIMPLE-MODEL FOR DESCRIBING THE DENSITY DEPENDENCE OF THE VIBRATIONAL-RELAXATION IN A POLYATOMIC NONASSOCIATED FLUID

A model is presented which allows the description of the density dependence of the vibrational relaxation in a fluid consisting of polyatomic molecules over a wide range of densities. In order to calculate the number of intermolecular collisions a molecule undergoes per unit time, use is made of the radial distribution function for a system of Lennard-Jones molecules as follows from molecular dynamics computer experiments. A density dependent energy exchange probability is introduced which partially compensates the influence of the steep increase in the intermolecular collision rate on the vibrational relaxation frequency above 350 amagats. Thus satisfactory agreement between theory and experiment can for instance be obtained between 0 and 600 amagats for CO2 at 25 and 50°C. © 1979 American Institute of Physics.