All molecules vibrate and Raman spectroscopy gives information on these vibrations in the form of a spectrum. Each spectrum is specific to the material being analysed.
The Raman effect is observed when a photon of light interacts with a molecule, exciting the molecule for a very short time (~10-14 s), before a second photon is scattered from the molecule as it relaxes. For most photons scattered, the wavelength of the scattered light will be equal to the incident light (Rayleigh scattering), however approximately one in a million photons (or less) exhibits a change in wavelength of scattered light to that of the incident light (Raman scattering). The energy difference between the incident and scattered light corresponds to the energy difference between two vibrational energy levels of the molecule. The scattering takes the form of a series of bands which can be related to the structure of the molecule.
The Raman effect is very weak due to the low number of photons scattered but Surface Enhanced Raman Scattering (SERS) is much more sensitive and can reduce fluorescence interference often observed using conventional Raman scattering.
