Calculation of collision induced energy transfer rates in tetrahedral molecules. Application to 12CH 4 perturbed by argon

Abstract

The semi-classical calculation of collisional energy transfer rates in spherical top molecules has been investigated. Multipolar transition moments are expressed in fully symmetrized tensorial form to allow realistic eigenfunctions (corresponding to the polyad structure of such molecules) to be easily incorporated. The short range intermolecular potential has been chosen as an atom-atom Lennard-Jones potential, following earlier studies in the framework of the semi-classical line broadening theory of Robert and Bonamy. A preliminary application to the bending dyad of methane perturbed by argon is reported. A sixth order expansion of the intermolecular potential has been used. The parameters were adjusted to fit observed line width measurements in the v 4 band. The results obtained for line widths and state to state energy transfer rates are discussed.