Vibrational Energy Transfer Rates Using a Forced Harmonic Oscillator Model

Abstract

This paper addresses the analysis, validation, and application of analytic, nonperturbative, semiclassical vibration-translation (V-T) and vibration-vibration-translation (V-V-T) rate models for atom-diatom and diatom-diatom vibrational molecular energy transfer collisions. These forced harmonic oscillator (FHO) rate models are corrected and validated by comparison with recent experiments, and with three-dimensional semiclassical trajectory calculations for N 2 -N 2 , O 2 -O 2 , and N 2 -O 2 , which are considered to be the most reliable theoretical data available. A remarkably good overall agreement is shown for both the temperature and quantum number dependence of single-quantum and double-quantum V-V-T transitions in the temperature range 200 < T < 8000 K and for vibrational quantum numbers 0 < ν < 40. It is demonstrated that the multiquantum vibrational energy transfer processes occur via a sequential FHO mechanism, as a series of virtual single-quantum steps during one collision. An important exception, asymmetric multiquantum V-V exchange at low temperatures, that occurs via a direct first-order mechanism, is discussed. Analytic thermally averaged FHO V-T and V-V rates are suggested. The FHO model gives new insight into vibrational kinetics and may be easily incorporated into kinetic modeline calculations under conditions when first-order theories are not applicable.