A new theory for vibrational and rotational energy transfer in the collisions of atoms with symmetric top molecules

Abstract

A new three‐dimensional quantum‐mechanical theory is described for calculating vibrational and rotational relaxation cross sections and rate constants for the collisions of atoms with prolate symmetric top or near‐symmetric top molecules. The technique uses a wave function expansion in vibrational states coupled with azimuthal basis functions which describe the spinning of the top about its symmetry axis. The infinite‐order‐sudden method is used for the total rotational angular momentum of the molecule. The technique is applied to the computation of vibrational relaxation rate constants for the collisions of C₂H₄ with He atoms. Comparison is made with results calculated previously by using the sudden approximation for both the total and azimuthal rotational motion. Good agreement is obtained with vibrational relaxation rate constants measured in an infrared double resonance experiment.