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.
Bibliographical noteFunding Information:
Support for this work was provided by NASA Ames Research Center under Cooperative Agreement No. NCA2-519 and by NASA Grant No. NAGW-1331 to the Mars Mission Research Center at North Carolina State University. Mr. Lan-drum was also supported by a National Defense Science and Engineering Graduate fellowship sponsored by the Air Force Office of Scientific Research, Boiling AFB, DC. Computer time was provided by the North Carolina Supercomputing Center. The authors thank S. P. Sharma, W. M. Huo, and C. Park for providing the vibrational matrix element programs and insight into the SSH formulation.
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