LOW-TEMPERATURE SOFT LIBRATIONAL MODE IN DIAMANTANE

A preliminary investigation is reported on the Raman spectrum of diamantane down to low temperatures. The spectrum shows the existence of a soft librational mode which goes to zero at Tc=35+or-2K. This phase transition occurs at the same temperature as a recently reported thermal anomaly. The phase transition is interpreted in terms of collective rotations of the diamantane molecules about their three-fold axes.