Raman Spectra of Crystalline CH4 and CD4

Abstract

The Raman spectra of crystalline CH₄ and CD₄ have been recorded in the temperature range 10°—77°K, which includes all three solid phases of CD₄ and Phases I and II of CH₄. Only three of the four Raman active fundamentals were observed in all cases and no lattice vibrations were seen. There are marked changes in the spectra at the transition Phase I—Phase II, but only small differences between the spectra of Phases II and III of CD₄. The spectra of Phase I are very similar to that of the liquid, suggesting that molecular rotation persists in the crystal at temperatures near the melting point. The structure of the fundamentals in Phase II is best interpreted in terms of a D_2d² space group. The more detailed spectrum for Phase III of CD₄ may be indicative of a lower symmetry, but alternative explanations are briefly discussed.