Raman Spectroscopy relies on inelastic scattering of visible light. It provides a finger print by which molecules can be identified. Any application where non-destructive, microscopic, chemical analysis and imaging is required. It can be used to characterize the chemical composition, and structure of any sample whether, solid, liquid, gas, powder, slurry, gel or paste.
Infrared Spectroscopy involves the interaction of Infrared (IR) light with the molecules in the sample. The sample can be solid, liquid or gas. It is a technique mostly based on absorption Spectroscopy. The energy of the infrared photons induces vibrational excitation of covalently bonded atoms and groups. The different vibrational modes of the molecules (bending, stretching, scissoring, rocking and twisting) are characteristic and unique. Infrared Spectroscopy is wildly used to identify organic compounds and unknown polymers. (used a lot in forensic studies & reverse engineering materials). One primary selection rule that influences the infrared absorptions, is that a, change in dipole moment should occur for a vibration to absorb infrared energy. Absorption bands associated with C=O bond stretching are usually very strong because a large change in the dipole takes place in that mode. On the other hand molecular symmetry & spectrometer limitations decrease the intensity of the IR peaks.