Classical or Wave Theory:

The concept of the polarisability of a molecule is fundamental to the understanding of the typical theory of Raman effect. Let us first know it before we move to the explanation of the Raman effect.

Polarisability of molecules

While a molecule is placed in a static electric field, the positive and negatively charged particles constituting the molecule get attracted to the opposite poles of the applied field. This leads to a charge separation and as a result to the development of an induced dipole moment. In easy words, we say in which the molecule has become polarised. This tendency of the molecule to get polarised is known as polarisability i.e., the ability to get polarised. The magnitude of the induced dipole moment is relative to the strength of the applied field and is given through the following equation.

µ = αE

The proportionality constant α is known as polarisability. It is a measure of the ease along with which the molecule (or a bond in it) could get polarised.