The Raman effect, named after Indian physicist Sir C. V. Raman who discovered it in 1928, is a phenomenon in molecular spectroscopy where light undergoes inelastic scattering upon interacting with matter. Specifically, when monochromatic light (light of a single wavelength) is incident on a sample, most of the scattered light has the same frequency as the incident light (Rayleigh scattering). However, a small fraction of the scattered light has different frequencies due to interactions with molecular vibrations and rotations in the sample.
The Raman effect occurs when incident light interacts with the vibrational and rotational modes of molecules, resulting in energy exchange between the incident photons and the molecules. The scattered light can have either higher or lower frequencies than the incident light, corresponding to Stokes and anti-Stokes Raman scattering, respectively.
Key points about the Raman effect:
Stokes Raman Scattering: The majority of Raman scattering results in photons losing energy and having lower frequencies than the incident light. This is known as Stokes Raman scattering.
Anti-Stokes Raman Scattering: A less common process involves scattered photons gaining energy and having higher frequencies than the incident light. This is called anti-Stokes Raman scattering.
Raman Spectroscopy: The Raman effect is widely used in analytical chemistry and materials science in a technique called Raman spectroscopy. In Raman spectroscopy, the scattered light is analyzed to provide information about the vibrational and rotational modes of molecules. This technique is valuable for identifying and characterizing molecular structures.
Energy Levels and Vibrational Modes: The Raman effect is related to the energy levels associated with molecular vibrations. When incident photons interact with a molecule, the energy transferred corresponds to the energy difference between the initial and final vibrational states of the molecule.
Raman spectroscopy is non-destructive and can be applied to study a variety of samples, including solids, liquids, and gases. It has widespread applications in fields such as chemistry, physics, biology, and materials science for the analysis of molecular structures and interactions.