Raman intensity analysis of LaCl₃ on lines adopted earlier for crystals like LiNO₃, KNO₃ or YVO₄ is found to be unsuitable for LaCl₃. The rotation of the LaCl₃ pyramids in the unit cell of this crystal is represented by high frequencies, comparable to the internal oscillations of LaCl₃ molecule. The intensity ofR_z, rotation about the symmetry axis of the crystal, is higher than the total symmetric line. These two factors show that the two molecules in the unit cell cannot be treated separately. Also, the polarisability of the bonds between atoms connecting the molecules cannot be neglected. The intensity formulae have been derived for this crystal and using the directional Raman spectra, electro-optical constants of the LaCl and Cl-Cl bonds have been evaluated. It is found that while the polarisability of Cl-Cl bond between the molecules, is about 0·4 times that of LaCl bonds, in crystals like LiNO₃ the polarisability of bonds like Li-O is found to be negligible.

A formalism to connect first-order Raman intensities of MgF₂ and its photoelastic constants is developed by developing a method of writing internal coordinates in terms of displacement gradientsu_ij which are not symmetric. It is found that for crystals containing only one line inA₁ species, the ratiosP₁₃/P₃₃ and (P₁₁ +P₁₂)/P₃₁ can be directly evaluated from the intensities, without having to derive the intensity formulae; while (P₁₁ +P₁₂)/P₁₃ is independent of the intensities as well as the refractive index of the crystal. It is a function of only the dimensional parameters. In this crystal, since the speciesB_1g andB_2g also contain only one line each, the ratio (P₁₁ −P₁₂)/P₆₆ can also be directly obtained from the intensities.