Vibrational relaxation and dissociation behind shock waves. Part 1 - Kinetic rate models.

Abstract

We address the validation of the analytical nonperturbative semiclassical vibration-translation and vibration-vibration-translation rate models for the atom-diatom and diatom-diatom vibrational energy transfer molecular collisions. These forced harmonic oscillator rate models are corrected and validated by comparison with three-dimensional semiclassical trajectory calculations for nitrogen, which are widely considered to be the most reliable theoretical data available. A remarkably good agreement is shown between the two models, for both the temperature and quantum number dependence of single-quantum and double-quantum vibration-vibration-translation jumps in the temperature range 200 < T < 8000 K and for vibrational quantum numbers 0 < v < 40. The simplicity of the theory, as well as the agreement shown, make the forced harmonic oscillator rate model attractive for master equation and direct simulation Monte Carlo modeling of nonequilibrium gas flows at very high temperatures, when the first-order, vibration-vibration-translation rate models are not applicable, and where use of the three-dimensional trajectory calculations is very cumbersome and time consuming. The forced harmonic oscillator model is also applied to obtain the probability of collision-induced dissociation of diatomics.