Raman and far infrared spectra of the two solid phases of methyl bromide: CH₃Br and CD₃Br

The phase transition in crystalline methyl bromide: CH₃Br and CD₃Br, has been studied by Raman spectroscopy. Spectra of the higher temperature a phase are reported here for the first time. The transition in CD₃Br is found to occur near 158 K, about 16 K lower than in CH ₃Br. Raman and far infrared spectra of the low temperature β phase at 20 K are also reported. Additional peaks in the lattice region and new splittings in the v₅ and v₆ regions have been observed. The spectra are assigned by means of a group theoretical analysis based on the known crystal structure of this phase and good agreement is obtained.