Classical theory of collisional depolarization and rotational relaxation in open-shell diatomic molecules

Abstract

The semiclassical S-matrix theory of Miller and Marcus is utilized to derive an exact classical mechanical expression for the effective cross sections governing collisional depolarization and rotational relaxation in open-shell molecules with Σ electronic symmetry. These cross sections are expressed as a sum of products of classical dynamical terms (which may be evaluated by conventional Monte Carlo techniques) and geometrical terms that describe the quantum mechanical coupling of the angular momentum vectors in the open-shell molecule. All effects on rotational transitions due to the nonzero electronic spin angular momentum in the open-shell molecule are accounted for through the geometrical terms. Recently, sophisticated molecular beam and laser double resonance techniques have allowed the state-resolved study of rotational energy transfer in collisions involving open-shell molecules in their ground electronic state. The present extension of classical scattering theory provides the theoretical framework for an exact classical mechanical calculation of the collision dynamics in such experiments.