Basics of vibrational spectroscopy

Infrared and Raman vibrational spectroscopies

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

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

Complementarity of IR and Raman spectroscopies

InfraredRaman
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
  • simple or no required preparation 
  • glass cells
Disadvantages
  • high absorption of glass, of H2O et de CO2
  • strong fluorescence
  • spectrum library still very incomplete
  • difficult quantitative analysis
  • less sensitive than the IR method
Sample type
  • Organic compounds
  • all
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