A simplified approach to the vibrational self-relaxation of simple molecules through convolution of their velocities

Abstract

A theoretical approach has been developed for computing collisional self-relaxation probabilities of the first excited level in the lowest vibrational mode of simple molecules. The bending (V2) vibration in triatomic molecules, in which the average translational and rotational velocities are of the same order of magnitude, was examined. The approach was based on the assumption that both the velocities should be taken into account as a convolution of the corresponding Maxwell's distribution functions. The model was checked for the SO2 molecule in the temperature range from 130-1100 K. The calculated temperature dependence curve (the Landau-Teller plot) exhibits a minimum at about 150 K. The data obtained is discussed in relation to some experimental results. The comparison indicates that the problem was treated in correct manner. Some additional aspects of the relaxation, like intermolecular interactions and the steric factor, are also briefly considered. It is believed that this approach offers quite a good basis for further improvements of theoretical treatments.