Vibrational spectra and phase transitions of crystalline bromoform

We have obtained the Raman and infrared spectra of bromoform crystals at different temperatures in the range −175 to 5 C. Under different experimental conditions, three crystalline phases are grown: α, stable between the melting point and −5 C; β, stable between −5 and −175 C, and γ, which can be trapped by sudden freezing of the liquid to liquid nitrogen temperatures. The γ phase transforms irreversibly into β at temperatures above about −80 C. Possible crystal structures for the three phases are discussed on the basis of the spectroscopic evidence. The results explain apparent contradictions in previously published spectra.