Vibrational Relaxation in Propane, Propylene, and Ethane

Abstract

Sound‐propagation measurements have been made in propane, propylene, and ethane at 30°C in the frequency/pressure range 0.16 to 1000 Mc/sec·atm. Vibrational relaxation was observed in all three gases. For propane and propylene single relaxation times, and for ethane two relaxation times, were observed experimentally. The relaxation time for propane is (1.56±0.08) 10^—8 sec and for propylene (1.48±0.08) 10^—8 sec at 1 atm. For ethane the observed relaxation times are (1.12±0.03) 10^—8 sec and (0.71±0.06) 10^—9 sec at 1 atm, the shorter being associated with the de‐excitation of the hindered rotational mode and the longer with the de‐excitation of the higher vibrational modes. Possible mechanisms for the de‐excitation of vibrationally excited propane, propylene, and ethane molecules are discussed in the light of these results.