Raman spectra and factor-group analyses of crystalline group IV tetrachlorides

Abstract

The Raman spectra of the crystalline molecular tetrachlorides of carbon, silicon, titanium, germanium, tin, and lead have been recorded at ca. 80 K. Factor-group analyses of the spectra are presented in terms of the symmetry group C_2h⁵ in which certain of the tetrachlorides are known to crystallise. Factor-group splitting is very much more pronounced for the ν₃(t₂) mode in each case than for the other fundamentals, this observation being in agreement with the predictions of the dipole coupling model. The structure of the ν₁(a₁) band is principally chlorine–isotopic in origin; however, for the heavier tetrachlorides the relative intensities of the components deviate significantly from those calculated, presumbly because of distortion of the band shapes by the presence of underlying hot bands.