Low energy vibrational relaxation of the diatomic molecule I2 (<i>B</i>) by collision with He

Abstract

A quantum mechanical study of the collision I2(B 3Π0 , n = 1, j = 0)+He→I2(B 3Π0 , n = 0, j′)+He is reported here. The initial relative kinetic energies are lower than 0.7 cm−1. The I2(B) diatom is approximated by a harmonic oscillator, while the atom–diatom interaction is described by two atom–atom Morse type potentials. The close-coupling equations for nuclear motion, within the body-fixed frame, have been solved numerically. The partial vibrational relaxation cross sections, corresponding to the J = 0,1,2 values of the total angular momentum, have been obtained as a function of energy. When several rotational channels in the n = 1 vibrational level are introduced in the calculation, resonances do appear with lifetimes of the order of several ps. These resonances enhance the efficiency of the collision. Their positions, at very low energies, cause the dependence of the mean cross section with increasing temperature to be a fast decreasing function, in agreement with experimental results.