Ultrasonic and Hypersonic Studies of Vibrational Relaxation in Benzene

Abstract

Ultrasonic absorption measurements have been made in benzene over the frequency range from 7 to 570 Mc/sec at 6° and 25° C. Velocity measurements at both ultrasonic and hypersonic frequencies also were made in the temperature range 6°–60°C. The observed relaxation effects may be interpreted in terms of double relaxation of the vibrational specific heat. Analysis of the absorption data indicates that the vibrational specific heat associated with all but the lowest vibrational mode relaxes in the ultrasonic range, with the measured relaxation frequency varying from 510 Mc/sec at 6°C to 560 Mc/sec at 25°C. Correlation of the ultrasonic and hypersonic data also indicates a second relaxation frequency (associated with the lowest vibrational mode) of the order of 10 Gc/sec.