Generalized Langevin equation approach for the rotational relaxation of a molecule trapped in a 3D crystal. II. Application to CO and CH3F in argon

Abstract

A numerical integration of the Langevin equations connected to the motions of a diatomic molecule trapped in a rare gas matrix is performed using a Runge–Kutta procedure and a Monte Carlo–Metropolis sampling for the initial configurations of the so-called primary system (cf. paper I). The rotational energy transfer from the molecule to the crystal is shown to strongly depend on the coupling between the molecule and the nearest-neighbor (NN) atoms and also on the ability for these NN atoms to dissipate their energy into the bath. Several cases are discussed according to the values of the viscous terms describing the damping of the molecule rotation and translation and of the NN atom vibrations. The prolate CH3F molecule trapped in an argon matrix seems to relax more quickly its rotational energy than the nearly isotropic CO molecule. Special trajectory calculations, when the molecule is rotationally excited or in thermal equilibrium, are considered in order to study the well jump and the librational motion of the CO molecule.