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(February 2011)| Raman scattering or the Raman effect (pron.:
//) is the inelastic scattering of a photon. It was discovered
by C. V. Raman and K. S. Krishnan in liquids, and by G.
Landsberg and L. I. Mandelstam in crystals. The effect had been
predicted theoretically by A. Smekal in 1923. When photons are
scattered from an atom or molecule, most photons are elastically
scattered (Rayleigh scattering), such that the scattered photons
have the same energy (frequency and wavelength) as the incident
photons. However, a small fraction of the scattered photons
(approximately 1 in 10 million) are scattered by an excitation,
with the scattered photons having a frequency different from,
and usually lower than, that of the incident photons. In a gas,
Raman scattering can occur with a change in energy of a molecule
due to a transition (see energy level). Chemists are concerned
primarily with such transitional Raman effect. The inelastic
scattering of light was