Diatomic molecules Raman scattering from

Rousseau, D.L. and Williams, P.F. (1976). Resonance Raman scattering of light from a diatomic molecule, J. Chem. Phys. 64, 3519-3537. 

Inelastic or Raman scattering of light can be understood classically as arising from modulation of the electron distribution, and hence the molecular polarizability, because of vibrations of the nuclei. For example, for a diatomic molecule, a can be represented adequately by the first two terms of a power series in the vibrational coordinate Q ... 

Fig. 1.32. Classical theory for the origin of the Raman effect. In (a) we see a diatomic molecule where represents protons and represents the center of gravity of the electrons. The electrons are displaced by the external field of the photon and an induced dipole moment is generated which changes when the bond length changes during the molecular vibration. The induced dipole moment is plotted in (b) as an amplitude modulated wave with steady amplitude components shown in (c) from which scattered radiation is generated.

Raman spectroscopy involves inelastic scattering of light instead of absorption or emission. The selection mles for Raman transitions are different from those of absorption and emission spectroscopy, so that many transitions that are forbidden in absorption and emission occur in Raman scattering. Raman scattering requires that the motion modulate the polarizability of the molecule. For rotational Raman transitions in diatomic and linear polyatomic molecules... 

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