Pressure dependence of excess ultrasonic absorption in CCl4

Abstract

Originally it was thought that the excess ultrasonic absorption (~) occurring in most of the associated liquids is due to thermal relaxation (2). The thermal relaxation is caused by the energy transfer from the external degrees of freedom to the internal degrees of freedom (thermal and vibrational) of a molecule. However, this failed to explain the results in water (3) and it was suggested that structural relaxation (4) may be the cause of the excess ultrasonic absorption. The structural relaxation being responsible for compressional viscosity we can estimate this b~ a knowledge of acoustic absorption. The study of compressional viscosity was first made by HIRAI and HYRING (5). They derived expressions for temperature and pressure dependence of compressional viscosity and could explain the excess absorption in some associated liquids. For the unassociated liquids, the separation o~ various contributions to ultrasonic absorption is comparatively difficult. In the present investigation, an at tempt has been made to separate the various contributions of ultrasonic absorption for CC14 as a function of pressure (e) at 30 ~ The total ultrasonic absorption in the case of unassociated liquids may be written as