Raman Spectra in Molecular Solids I. A study of Low Frequency Modes as a Funcit of Temperature

The study of the low frequency modes in some molecualr solids as a functio of temperature shows a drastic decrease of these frequencies as the melting temperature is approached. These results provide a demostration of the validity of the theroy, illustrated by calculatios of Cochran and Rosenstock, according wihich the occurrence of certain phase changes should be accompanied by a decrease or a vanishig of some intermolecular force constants. Furthermore our results allow a tentative discrimination between external and internal modes.