Raman and infrared spectra of some tetrahalide crystals

Recent Raman and infrared spectra of a number of tetrahalide crystals are reported. While some examples of isotopic and crystal field splittings of the internal molecular modes are included, the emphasis is on the external lattice vibrations which are important for investigations of intermolecular forces and lattice dynamics calculations. Because of the weak signals from these non-polar near-spherical molecules and other experimental difficulties, these modes have not been investigated in detail in earlier work. Examples to be discussed include CCl₄, CBr₄ and CF₄, all of which exhibit solid state phase transitions; the tetrachlorides of Ge, Ti, Si and Sn, all of which are thought to have similar crystal structures; and SnBr₄, the structure of which is accurately known and is used as a basis for lattice dynamics calculations.