Transition dipole moment basic concepts

In the classical description, the appearance of the polarization of angular momenta of molecules in absorption is determined, on the one hand, by the manner in which the oscillations of the light vector E and the absorbing dipole d are mutually positioned on the other hand, it is determined by the way in which this dipole is tied to the molecular structure. 

In the process of scattering and absorption, the electric component of the incident wave excites the vibrations of the oscillator. Under the effect of this component the electron performs forced vibrations. If the eigenfrequency ojq of the oscillator coincides with that of the light wave u i, resonance absorption is observed. If these frequencies do not coincide, we have non-resonant scattering of light. 

In addition, it ought to be kept in mind, considering the classical concept of light absorption by molecules, that, owing to the inertia of molecules, the light field is not capable of turning the molecule and thus excites the vibrations of the dipole oscillator only to the extent to which 

---