What are stokes and anti-stokes lines in raman spectrum. Explain how these lines are emitted. (It was a 6 marks question in my preboard so answer accordingly)

Dear Student,

Strokes lines are associated with a radiation of the particular wavelength which is present in the spectra formed during Raman Effect.Stokes lines are of longer wavelength than that of the exciting radiation responsible for the fluorescence or Raman effect.These lines emit when the vibrational level of atoms starts from virtual state and end at a level which is just before ground electronic state.

Anti strokes lines are found when atoms or molecules of the material are already in the excited state. The radiated line energy, in this case, is the sum of the pre-excitation energy and the energy absorbed from the exciting radiation. Hence, anti-Stokes lines are always of shorter wavelength than that of the light that produces them.
These lines emit when the vibrational level of atoms starts from virtual state and ends perfectly at ground electronic state.
Regards