Which phenomenon deals with the scattering of light by molecules of a medium when they are excited to vibrational energy levels?

Raman Effect

The correct answer is option 3. Raman Effect.

The phenomenon that deals with the scattering of light by molecules of a medium when they are excited to vibrational energy levels is called the Raman Effect.

The Raman Effect, named after the Indian physicist Sir C.V. Raman who discovered it in 1928, refers to the inelastic scattering of photons by molecules. When light interacts with molecules, some of the scattered light has wavelengths different from that of the incident light. This shift in wavelength is caused by the transfer of energy between the incident photons and the molecules, typically due to vibrational or rotational transitions within the molecules. The Raman Effect is widely used in spectroscopy to study molecular structure, chemical bonding, and other properties of materials.