Analysis Of Raman Spectroscopy

2.5.1 Raman Spectroscopy

Inelastic scattering of light by elementary excitations such as phonons and plasmon in the material is termed as Raman scattering. When a beam of light (UV-Visible and IR region) of frequencyI is incident on a solid, most of the light gets scattered elastically, i.e., without change in energy. A small fraction of light is scattered inelastically with frequencies I ± m, where m are the characteristic vibrational frequencies of the e- cloud in the molecule/solid. Figure. 2.8 Schematic view of the elastic and inelastic processes in a material with incidence of light.

The spectral bands with frequencies I-m are called Stokes Raman bands whereas and those of I+m are called anti-Stokes. Thus the energy differences between the incident and the Raman scattered photons are equal to the frequencies of lattice vibrations or phonons.

Quantum theory of Raman scattering

Quantized lattice vibrations are called phonons. There

; laser polarized parallel to a Y axis; analyzer set to pass X polarized light

Therefore, in the case of an anisotropic or unknown sample, it is recommended to record the Raman spectra with all the above motioned four polarization configurations.

Raman polarization

The three dimensional frame of reference can be used to describe the orientation of incident light with respect to that of the target sample specimen. The electric field component of the em light can be resolved into three mutually perpendicular orientations namely Ex, Ey, and Ez. Similarly, the polarization vectors of the sample can be resolved into Px, Py, and Pz to describe the dipole induced by the light in the target material. The electric field and polarization vectors are related by a 3×3 matrix called the polarization tensor,4

Hendra, P.; Jones, C.; Warnes, G. “The vibrational behaviour of molecules”, in Fourier Transform Raman Spectroscopy Instrumentation and Chemical Applications; Ellis Horwood Ltd.: Chichester, England, 1991. ; …..…..