What is Raman spectroscopy?

Raman Spectroscopy is a non-destructive chemical analysis technique which provides detailed information about chemical structure, phase and polymorphy, crystallinity and molecular interactions.  It is based upon the interaction of light with the chemical bonds within a material.

Raman is a light scattering technique, whereby a molecule scatters incident light from a high intensity laser light source. Most of the scattered light is at the same wavelength (or colour) as the laser source and does not provide useful information – this is called Rayleigh Scatter.  However a small amount of light (typically 0.0000001%) is scattered at different wavelengths (or colours), which depend on the chemical structure of the analyte – this is called Raman Scatter.

Water molecule

A Raman spectrum features a number of peaks, showing the intensity and wavelength position of the Raman scattered light.  Each peak corresponds to a specific molecular bond vibration, including individual bonds such as C-C, C=C, N-O, C-H etc, and groups of bonds such as benzene ring breathing mode, polymer chain vibrations, lattice modes etc.

A typical Raman spectrum, in this case of aspirin (4-acetylsalicylic acid). The inset image shows the detail which is present in the spectrum.
A typical Raman spectrum, in this case of aspirin (4-acetylsalicylic acid). The inset image shows the detail which is present in the spectrum.
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