Basic Theory of RS

Raman spectroscopy is a vibrational optical spectroscopic technique based on the inelastic scattering of light by matter like the molecule of interest. Raman spectroscopy is a highly specific technique due to specific molecular fingerprint information as observed in the Raman spectra. This phenomenon was theoretically predicted by Smekal in 1923 (Smekal 1923). In 1928, the first experimental observation of RS effect was reported by Indian physicists C.V. Raman and K.S. Krishnan (Raman and Krishnan 1928a, b) and independently by Mandelstam and 

Landsberg in the former Soviet Union (Mandelstam and Landsberg 1928). In the experiment of C.V. Raman sunlight was focused by a telescope onto a sample which was an organic liquid (solvents) or vapour. The scattered radiation was collected by a second lens and by a system of optical filters. In 1930, C.V. Raman earned the Nobel prize in physics for his work on the scattering of light and for the discovery of the effect named after him . More details about history of the discovery of Raman effect can be found in the paper of Krishnan and Shankar (Krishnan and Shankar 1981). 

Since the Raman effect is intrinsically quite weak, relatively high-power lasers and sophisticated optical and electronic equipment are required to detect the Raman scattered photons. This accounts for the lengthy time that elapsed in the development of Raman spectroscopy. It experienced a rebirth in the 1960s with the invention of laser and its use as a light source. However, from the 1980s the advances in optoelectronics, particularly the development of compact lasers, detectors and efficient optical filters allowed lower cost, integrated instmments to be produced commercially. Consequently, Raman spectroscopy has been adopted as a routine method in many fields because it has been shown to be simpler and faster than alternative techniques. 

1 Simplified Jablonsid diagram illustrating the Rayleigh, NRS and RRS processes and ctmesponding Raman spectrum of CCI4, v-the vibrational quantum numbers 

Light scattering processes are related to the polarizability of the molecule which interacts with the EM field. A simple classical EM field description of Raman spectroscopy can be used to explain many of the important features of Raman band intensities. The incident EM field Eioc(ci inc). induces a dipole moment pind in the molecule proportional to the molecular polarizability amoiecuie  

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