Knowledge Bank

The Raman spectra of crystalline $CH4$ and $CD4$ have been recorded in the temperature range $10\circ -77\circ K$, 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. The spectrum of Phase I near the melting point is very similar to that of the liquid, suggesting free or nearly free rotation. The structure of the fundamentals in Phase II is best interpreted in terms of a $D2d$ crystal symmetry. The spectrum of Phase III of $CD4$ shows little difference from Phase II and so is inconclusive.