Effect of VV Transfer on the Rate of Diatomic Dissociation

The effect of VV transfer processes on the rate of thermal dissociation of diatomic molecules is considered within the steady-state approximation for a single-quantum step master equation. An accurate rate law is obtained for the truncated harmonic oscillator through replacement of the agents for VV transfer by the vibrational energy. Approximate numerical solutions for a Morse oscillator model of the representative species O2, H2, and HCl are in quite satisfactory agreement with the measured rates and provide at least qualitative explanations for nearly all the unusual features of the measurements. The rate enhancement effect of VV transfer is found to be slight; the primary, and quite general consequence of VV transfer is rather a depression of the rate, especially at high temperatures, which then appears as a considerable reduction in activation energy. This effect is shown to arise from a violation of detailed balance for the VV processes whenever the vibrational energy is depleted by rapid dissociation.