Selection Rules
The distortion of a molecule in an electric field, and therefore the vibrational Raman cross section, is determined by its polarizability.
A Raman transition from one state to another, and therefore a Raman shift, can be activated optically only in the presence of non-zero polarizability derivative with respect to the normal coordinate (that is, the vibration or rotation):
Raman-active vibrations/rotations can be identified by using almost any textbook that treats quantum mechanics or group theory for chemistry. Then, Raman-active modes can be found for molecules or crystals that show symmetry by using the appropriate character table for that symmetry group.
Read more about this topic: Raman Scattering
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