Ultrasonic Relaxation and the Vibrational Specific Heat of Carbon Disulphide

Previous work has shown that the absorption of ultrasonic waves in liquid carbon disulphide is governed by a relaxation mechanism. The measurements reported from this work were made below the frequency of 70 Mc/s, which is near the centre of the dispersion range at 25°C. Combining these results with others reported by Rapuano in the frequency range 75Mc/s to 195Mc/s, led to the conclusion that the observed behaviour was associated with the time of transfer of energy to the degenerate bending vibration of the carbon disulphide molecule. Quantitative analysis of the results, however, was not regarded as satisfactory. Measurements of the absorption of ultrasonic waves in carbon disulphide have now been made by the authors at frequencies up to 190Mc/s and at different temperatures. The results obtained do not agree with Rapuano's particularly at the higher frequencies so that his measurements have been discarded. Analysis of the complete experimental results now available at both 25°C and - 63°C shows conclusively that the anomalous absorption in carbon disulphide is due to the relaxation of the total vibrational specific heat as described by a single relaxation time. Moreover, the absorption at frequencies well above the relaxation region appears to be determined by the `classical' mechanisms of shear viscosity and thermal conduction.