On the Derivation of Reaction Parameters from Observations of Ultrasonic Relaxation

Abstract

Measurements of ultrasonic relaxation in liquids and gases provide experimental data from which it is desired to obtain theoretically useful parameters such as heats of reaction and transition probabilities. It is shown here that even if full experimental results are available concerning the variation of the ultrasonic relaxation strength r with pressure and temperature it is still necessary to make at least three assumptions before thermodynamic reaction parameters can be evaluated. The main purpose of the paper is to set out a logical theory which makes the nature of these assumptions explicit. It is first shown how the experimental results can best be analysed to yield the relaxation strength. The formula connecting the relaxation strength with the reaction parameters leads to a partial differential equation which is integrated in a form convenient for practical application. The general implications of the theoretical work are discussed in relation to experimental observations and the need for further experimental work at high pressures is emphasized.