Rotational relaxation in mixtures of methane with helium, argon and xenon

Abstract

Measurements of ultrasonic absorption have been made in binary mixtures of methane with the noble gases helium, argon and xenon. The absorption coefficients were measured in a single-crystal interferometer at a frequency of 3.001 MHz and a temperature of 308.3 K in the pressure range from 100 to 150 torr. Rotational relaxation times and numbers were derived from the observed absorption. The estimated collision numbers for translational-rotational energy exchange are: Z rot ( CH 4− CH 4) = 12.3, Z rot ( CH 4− He) = 3, Z rot ( CH 4− Ar) = 12, Z rot ( CH 4− Xe) = 27. Calculations of rotational relaxation numbers Z rot of spherical top molecules in an inert gas have been made by Widom and Sather and Dahler. Although their values are higher, they predict the same tendency as we found experimentally.