Energy Transfer by Collision in Benzene Vapor

Abstract

The velocity and absorption of ultrasonic waves in benzene vapor were measured by means of the sonic interferometer, at frequencies of 251.44 kc, 497.44 kc, and 1008.06 kc, within the pressure range 2 to 9.5 cm Hg, between the temperature limits 30.2°C to 37.6°C. Dispersion of the velocity, after being reduced to 30°C, ranged from 190.4 m/sec to 207.31 m/sec. The corresponding values of the specific heat Cv/R dropped from 9.45 to 3.0. Values of the molecular absorption coefficients, which are several times larger than the classical ones, are interpreted as due to the loss of vibrational degrees of freedom only. The theoretical values calculated from Kneser's method, show a close agreement with the dispersion curve, but not so well with the absorption values. An improvement of fit was made by the assumption of two relaxation times, but owing to the scattering of the experimental points, it is very hard to decide which theory fits better. The value of the single relaxation time is 5×10−8 sec, and those from the second assumption are 2×10−8 sec and 6.8×10−8 sec.