Transfer of vibrational-rotational energy in thermal reactions: application to polyatomics

Abstract

A simple model is used to deal with vibrational-rotational energy transfer in a thermal dissociation of a polyatomic molecule under non-equilibrium conditions when collisional energy transfer is rate-determining. Transition probabilities are assumed to be factorizable into purely vibrational and purely rotational terms, both given by an exponential model; a gaussian model is also used for the vibrational term. The master equation leads to a two-dimensional integral equation which is solved by means of the so-called “fixed-υ” approximation developed previously, in which no vibrational energy transfer takes place while rotational energy is being transferred. Two sets of calculations are performed, one with rotational energy transfer much faster than vibrational energy transfer, and the other with both of equal importance. Relative to purely vibrational energy transfer, rotational energy transfer is shown to lead to increased rate of dissociation and increased depopulation of levels near threshold, especially in the first set of calculation, and also to a further decrease of activation energy below the bond-dissociation energy. The model system used is the dissociation of H 2O 2 and the calculated data are in good agreement with experiment where available.