Basics of vibrational spectroscopy

Infrared (IR) and Raman spectroscopies are complementary vibrational spectroscopies which allow for the characterization of the molecular composition of a substance. They are often non-destructive, require little preparation and a small amount of product.

These analytical techniques are applied in many fields: quality control, food industry, art, forensics, and space.

	Infrared	Raman
Physical phenomenon	absorption  variation of dipole moment (intense bands caused by ionic bonds: O-H, N-H…..)	scattering change of polarizability (intense bands caused by covalent bonds: C=C, C-S, S-S…)
Sample processing	thickness: very thin for transmission good contact for ATR	no contact with the sample non-destructive little or no preparation   glass cells
Disadvantages	high absorption of glass, of H2O and of CO2	intense fluorescence spectra library still very incomplete difficult quantitative analysis less sensitive than the IR method
Sample type	Organic compounds	all