Vibrational relaxation of anharmonic oscillator molecules. II. Non- isothermal conditions

Abstract

For pt. I see abstr. A43263 of 1968. A previously published theory describing the vibrational relaxation of a system of anharmonic oscillator diatomic molecules has been extended to cover situations in which a continuously changing translational temperature is imposed on the gas. With this extension, the theory is applicable to the results of recent experiments in which vibrational relaxation has been studied in expanding gas flows, several of which have indicated anomalously fast rates of de-excitation in N₂ and CO. Calculations including the effects of rapidly falling translational temperature have been performed for CO. It has been found that near-resonant vibration-vibration exchanges continuously distort the vibrational distribution function in response to the changing translational temperature. This distortion does not contribute to the vibrational de-excitation of the gas, since the vibrational exchange processes do not remove vibrational quanta from the molecules. However, in an expanding flow it causes a continuous reduction in the vibrational 'temperature' of the 1 to 0 transition and can therefore give the appearance of a rapid rate of de- excitation. An empirical expression for the apparent rate of de-excitation is given in an appendix.