Vibrational Relaxation in Methane—Oxygen Mixtures

Measurements have been made of the relaxation frequency and vibrational specific heat of mixtures of oxygen and methane, with the methane concentration varying from 0.05% to 1.6%. The temperature in all cases was 23°C and the total pressure of the mixture atmospheric. Results of these measurements show that the relaxation frequency does not vary linearly with methane concentration and that the vibrational specific heat is concentration dependent. Theoretical interpretation of these results indicates that there is a strong coupling of the vibration of oxygen to that of methane and that losses due to radiation from the methane are significant. It is further determined that methane is approximately as effective in exciting vibration in oxygen as in itself and that oxygen is considerably less efficient in exciting vibration in methane. Supplementary measurements were also made on pure methane and methane dilute in gases characterized by their vibrational inertness — N2, Ne, Ar, and Kr. The relaxation time of pure methane was found to be in excellent agreement with values determined by previous investigators. Nitrogen was found to have a measurable effect in shortening the relaxation time of methane; surprisingly, Ne, Ar, and Kr were all found to be more effective than nitrogen.