Raman scattering is a fundamental optical phenomenon where light interacts with molecules and gets scattered with a different frequency than the original incident light. When a laser beam hits a molecule, most light scatters elastically with no frequency change, but a small fraction undergoes inelastic scattering, where energy is exchanged between the photon and the molecule's vibrational modes.
In Raman scattering, energy exchange between photons and molecules creates two distinct types of scattering. In Stokes scattering, the molecule absorbs energy from the photon and moves to a higher vibrational state, resulting in scattered light with lower frequency than the incident light. Conversely, in anti-Stokes scattering, the molecule transfers energy to the photon, moving to a lower vibrational state and producing scattered light with higher frequency.
A Raman spectrum displays the characteristic frequency shifts that occur during scattering. The central Rayleigh peak represents elastic scattering with no frequency change. Stokes lines appear at lower frequencies, indicating energy loss from photons to molecular vibrations. Anti-Stokes lines appear at higher frequencies, showing energy gain from molecular vibrations to photons. The magnitude of these frequency shifts directly corresponds to the vibrational frequencies of the molecule, making Raman spectroscopy a powerful tool for molecular identification.
Raman spectroscopy has diverse applications across multiple fields. In material science, it analyzes crystal structures and measures stress and strain in materials. Chemists use it for molecular identification and determining chemical composition. In biology and medicine, Raman spectroscopy enables non-invasive tissue analysis and disease diagnosis. The pharmaceutical industry relies on it for drug quality control and studying different crystal forms of medications. This versatility makes Raman spectroscopy an invaluable analytical tool in research and industry.
To summarize what we have learned about Raman scattering: It is a fundamental optical phenomenon involving inelastic interactions between light and molecules. Energy exchange during scattering creates characteristic frequency shifts that reveal molecular vibrations. This makes Raman spectroscopy a powerful analytical technique with applications across multiple scientific and industrial fields.