Growth, characterisation and ultrasonic studies of a rotator-phase solid, carbon tetrabromide

Abstract

Ultrasonic Velocity measurements are reported as a function of temperature on single crystals of the monoclinic phase of carbon tetrabromide up to and including the rotator phase transition. A marked drop in the velocity consistent with an increase in the compressibility of the sample was observed at 320.9 K. Differential scanning calorimetric studies confirm that a transition occurs at this temperature and that the crystal melts at 366.4 K. These data are in agreement with previous reports on the phase behaviour of these crystals and confirm the existence of the rotator phase. The onset of rotator phase motion is accompained by a marked increase in the acoustic attenuation which is associated with the possibility of two facile rotational–vibrational energy transfer processes occurring in the rotator solid state.