Raman effect Raman and Krishnan studied extensively, the scattering of light by solids liquids and gases. They observed that the scattered light contains faint lines of frequency different from the incident light. This is called Raman effect.
The explanation of Raman effect follows from the quantum theory. An incident light photon of energy hn impinges upon an atom or molecule of the scattering medium. The energy state of this atom or molecule changes from E1 to E2. Then the energy of the scattered photon is given by,
hn - ( E2 - E1)
If n ´ is the frequency of this scattered photon, then
hn ´ = hn - ( E2 - E1)
( E2 - E1)/h = n -n ´ (r4)
The difference between frequency of each Raman line and the frequency of the incident light is thus equal to the frequency of some emission or absorption line of the scattering atom or molecule.
Transitions that are forbidden in ordinary spectra occur freely in Raman effect. The atomic or molecular energy states which cannot be studied using normal technique, can be investigated by Raman effect. Therefore Raman effect is an important tool for the study of quantum states of molecules and also for the chemical analysis.