[1] Early work in this field was carried out by George Placzek, who developed the theoretical treatment of bond polarizability.
The value of the depolarization ratio of a Raman band depends on the symmetry of the molecule and the normal vibrational mode, in other words, the point group of the molecule and its irreducible representation to which the normal mode belongs.
[4][5] For a spherical top molecule in which all three axes are equivalent, symmetric vibrations have Raman spectral bands which are completely polarized (ρ = 0).
However, for the asymmetric mode in which one C−H bond stretches while the other three contract, the Raman scattered radiation is depolarized.
[4] For molecules of lower symmetry (symmetric tops or asymmetric tops), a vibration with the full symmetry of the molecule leads to a polarized or partially polarized Raman band (ρ < 0.75), while a less symmetric vibration yields a depolarized band (ρ ≥ 0.75).