Ultrasonic dispersion in gaseous sulphur dioxide

The velocity of ultrasonic waves has been measured in gaseous sulphur dioxide at 20, 102 and 200° C for values of f/p ranging from 200 kcs-1 atm-1 to 7 Mcs-1 atm-1. (f is the ultrasonic frequency, p the pressure.) Dispersion involving the major part of the vibrational specific heat was found at all temperatures. Each dispersion zone corresponds to two distinct relaxation times differing by a factor of ten. The lower relaxation time corresponds with activation of the lowest (519 cm-1) vibrational mode, the higher to activation of the remainder of the vibrational energy. The conditions giving rise to a double relaxation process are discussed.