Raman Spectroscopy Essay

Raman spectroscopy utilises inelastic scattering of monochromatic light to generate Raman spectra which provides useful information pertaining to crystal structures. In this technique, laser light is utilized as a source to irradiate the sample. Photons of the laser light are absorbed by the sample and then re-emitted. The frequency of the re-emitted photons either gets increased or decreased in comparison to the original monochromatic frequency, which is termed as Raman effect. This shift provides information about vibrational, rotational and other low frequency transitions in molecules. Raman spectroscopy can be used to probe solid, liquid and gaseous samples. The characteristic fingerprinting pattern in a Raman spectrum enables identification of substances including polymorphs and also evaluation of local crystallinity, orientation and stress.

Raman spectroscopy has some distinctive advantages such as:

 Non-contact and non-destructive analysis

 High spatial resolution up to sub-micron scale

 Both organic and inorganic

This state is unstable and the photon is quickly re-radiated as scattered light. The scattering may be either elastic (Rayleigh) or inelastic (Raman) mechanisms. Raman scattering may be bifurcated into two categories: Stokes and anti-Stokes. Stokes Raman scattering is a process wherein an electron is excited from the ground level and falls to a vibrational level. It involves energy absorption by the molecule and therefore Stokes Raman scattered light has lesser energy (longer wavelength) in comparison to the incident light. In variation, anti-Stokes Raman scattering is a process in which an electron is excited from the vibrational level to the ground level. It involves an energy transfer to the scattered photon thus anti-Stokes Raman scattered light has greater energy (shorter wavelength) than incident