Fine structure of the Raman lines of carbon tetrachloride

Assuming first of all for simplicity that the four chlorine atoms are identical, the greatest symmetry the CCl4 molecule could have is Td. This would lead us to anticipate four fundamentals, v1, v2, v3, v4 belonging to normal modes A1, E, F2, F2, respectively, using Placzek’s (1934) nomenclature. A1 is the total symmetric normal mode, and so v1 is polarized in the Raman effect, and inactive in the infra-red. A1 is a singlet mode. E is a doublet mode and v2 is depolarized in the Raman effect, while it is inactive in the infra-red. F2 is a triplet mode and v3 and v4 are depolarized in the Raman effect and are also active in the infra-red. If the Raman spectrum of CCl4 is examined under coarse dispersion, lines are observed at 217, 314, 459 cm.-1, identified as v2, v4 and v1 respectively. Two at 760 and 790 cm.-1 are usually regarded as the result of resonance degeneracy between v3 and (v1 + v4), both in the mode F2.