Theory of distortion-induced I.R. and Raman intensity of forbidden modes of molecular units in crystals: II. Non-polar site symmetry case

Using the principles of group theory and approximation methods, a quantitative theory of distortion-induced infrared and Raman intensity due to forbidden modes of molecular units at non-polar site symmetries in crystals has been discussed. Among all forbidden modes only those which belong to , attain distortion induced activity (DIA) of first order where α ij / an is a component of anisotropic polarizability tensor; others attain higher order DIA and are hardly expected to be observed in I.R./Raman spectra due to their weak intensity.