By Sunil Bhardwaj

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According to basic quantum theory, there is collision between the molecules of reactants and that of photons of the radiations. The collisions are of the following three types.

1) Elastic Collision: In this collisions, when the photons are colliding the, molecules neither gain nor loose the energy. This is perfectly elastic collisions and the scattered radiations will have the same frequency as that of incident and is known as Rayleigh scattering.$$ { \nu }_{ scattered }={ \nu }_{ incident } $$

2) InElastic Collision: In these types of collisions the photon either gains the energy or looses the energy:

a) At the time of collisions photons lose their energy to molecules so than the scattered radiations will have less energy, means ( { \nu }_{ scattered }\) is less than \({ \nu }_{ incident }\).$$ { \nu }_{ scattered }<{ \nu }_{ incident } $$This results in Stoke’s lines.

b) During the collisions molecules lose energy to photons, so the scattered radiation will have more energy means \( { \nu }_{ scattered }\) is more than \({ \nu }_{ incident }\).$$ { \nu }_{ scattered }>{ \nu }_{ incident } $$This results in the Antistoke’s lines.

Polarisibility in a molecule