Raman intensity analysis of LaCl3

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.