Mechanisms for Vibrational Relaxation at High Temperatures

Abstract

Attention is called to several mechanisms which effectively couple translational and vibrational motions through the intermediary of chemical reactions. It is proposed that these processes lead to shorter relaxation times than those expected from direct energy exchange via inelastic collisions. Quantitative estimates are made, and relaxation times for these different processes are compared as a function of the reciprocal temperatures. At high temperatures, it is proposed that the transfer of energy from rotations to vibrations at approximately constant total energy can be induced by distant collisions. These serve primarily to balance the change in rotational angular momentum. Such events provide alternate paths for rapid vibrational relaxation, particularly for the upper vibrational levels, and may account for the fact that the observed rates of dissociation are considerably higher than the rates calculated under the assumption that these are limited by vibrational equilibration via inelastic collisions.