VIBRATIONAL-ENERGY TRANSFER RATES USING A FORCED HARMONIC-OSCILLATOR MODEL

This paper addresses the analysis, validation, and application of anal ytic, nonperturbative, semiclassical vibration-translation (V-T) and v ibration-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 valida ted 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 avail able. A remarkably good overall agreement is shown for both the temper ature and quantum number dependence of single-quantum and double-quant um V-V-T transitions in the temperature range 200 less than or equal t o T less than or equal to 8000 K and for vibrational quantum numbers 0 less than or equal to upsilon less than or equal to 40. It is demonst rated that the multiquantum vibrational energy transfer processes occu r via a sequential FHO mechanism, as a series of virtual single-quantu m steps during one collision. An important exception, asymmetric multi quantum V-V exchange at low temperatures, that occurs via a direct fir st-order mechanism, is discussed. Analytic thermally averaged FHO V-T and V-V rates are suggested. The FHO model gives new insight into vibr ational kinetics and may be easily incorporated into kinetic modeling calculations under conditions when first-order theories are not applic able.