Ultrasonic relaxation in gaseous sulphur hexafluoride and tungsten hexafluoride

Abstract

A pulse technique has been used to measure vibrational relaxation times in sulphur and tungsten hexafluorides. Despite the large differences in molecular weight, the relative relaxation times are as predicited by the general theory of vibration–translation energy transfer. There is no evidence that vibration–rotation transfer is important, or that the unusual mass of the central atom causes unforeseen effects. On the other hand, the vibrational relaxation is more efficient than predicted by a priori calculation (using quantities derived from low-energy collisional phenomena) as is frequently found for polyatomic molecules.