Vibration-dissociation coupling in nonequilibrium flows

The nonequilibrium vibrational relaxation of a system of rotationless nitrogen molecules is simulated when instantaneously heated or cooled under constant volume and temperature constraints. A set of coupled vibrational master equations including vibration-vibration and vibration-translation exchanges, dissociation, and recombination, is numerically integrated. Exchange rates are based on Schwartz, Slawsky, and Herzfeld theory as modified by Keck and Carrier. Molecules are described by the analytic Huxley-Murrell potential. Transition rates are found to be strongly influenced by the inverse range parameter. In the heating case, transfer rates to the upper levels, reach an approximate balance with the free state resulting in a constant dissociation rate. For the cooling case, the upper levels quickly equilibrate with the free state near the translational temperature. But, these populations were significantly higher than those expected at equilibrium, signifying a population inversion. In both cases, the observed behavior is believed to be due to an inhibition of the transfer of molecules between the upper and lower vibrational levels.