Raman and infrared studies of the lattice vibrations of some halogen derivatives of methane

Low frequency Raman and far infrared spectra of some crystalline halogen derivatives of methane, CH n X 4-n (n=0 to 3, X=F, Cl, Br or I), are presented and reviewed. Results are analysed in terms of the predictions of group theory, based on the molecular and crystal structures. The use of deuterated species to aid In the assignment of the observed spectra is discussed. Of particular interest are certain molecules which exhibit phase transition in the solid state, either reversible or irreversible in nature. Changes in spectra as a function of temperature are described In several cases. Prospects for future lattice dynamics calculations on these crystals are briefly outlined.