The Difference between Raman and Infra-red Spectroscopy

Infrared ( IR ) and Raman Spectroscopy are both used to identify unknown molecular structures and are based on the vibrational energy transitions of the molecules. The Raman technique detects the spectra of the light scattered elastically and inelastically from the sample, while the IR technique is based on the absorption lines appearing on the infrared spectrum. One of their main differences is that the Raman signal is evident when the polarizability of the molecule changes, while for the IR signal the molecule must undergo dipole moment change. In practice, Raman spectroscopy complements Infra-red spectroscopy and vice versa.