Dissociation of diatomic molecules. I. Effect of limited numbers of rotational states

Abstract

The rate of dissociation of a diatomic molecule is derived from a simple collision model. The diatomic molecule is treated as a rotating vibrator with a limited number of allowed rotational states in the upper vibrational levels. Limiting the number of rotational levels causes the population of the upper vibrational levels to increase more slowly with temperature than for a harmonic oscillator. This in turn causes the dissociation rate to increase more slowly than predicted by the expression exp(− D/R T), where D is the dissociation energy of the molecule. It is found that the dissociation rate depends strongly on the collisional dissociation probability but the activation energy does not. The model is applicable to situations where there is a Boltzmann translational energy distribution and a nonequilibrium vibrational distribution characterized by a vibrational temperature. The dissociation rates of H2 and HF are considered as specific examples.