What phenomenon earned C. V. Raman the 1930 Nobel Prize in Physics?

The Raman effect earned C. V. Raman the 1930 Nobel Prize in Physics.

The Raman effect is the inelastic scattering of light by matter. Most scattered photons retain the incoming light's energy, but a small fraction exchange energy with molecular vibrations or other excitations. The resulting frequency shifts reveal information about a substance's structure.

Raman and his collaborator K. S. Krishnan reported the effect in 1928 while working in India. Their experiments used sunlight and optical filters before the widespread availability of modern lasers. The discovery established a powerful form of spectroscopy.

The Raman effect is sometimes confused with the Compton effect, another scattering phenomenon recognized by a Nobel Prize. Compton scattering involves high-energy photons and electrons, whereas Raman spectroscopy commonly examines vibrational states in molecules.