CHILAKAPATI  LAB

 

Welcome to the world of vibrational spectroscopy application in cancer


Sir C.V. Raman

The Raman effect was named after one of its discoverer, the Indian scientist sir C.V. Raman who observed the effect by means of sunlight in 1928 [ ].He was honored with noble prize in 1930 for his discovery using sunlight as the source and a telescope as a collector ; the detector was his eyes.hence the discovery of such a feeble phenomenon using crude instrumentation was indeed a remarkable achievement. He explored that the wavelength of a small fraction of the radiation scattered by certain molecules differ from that of the incident beam; furthermore, the shift in wavelength depend upon  the chemical structure of the molecules responsible for scattering. The shift in energy gives information about the vibrational modes of the molecules. Hence, Raman spectroscopy is a form of vibrational spectroscopy.
The Nobel Prize in Physics 1930
Sir Chandrasekhara Venkata Raman
for his work on

"the scattering of light and for the discovery of the effect named after him"
 


A New Type of Secondary Radiation
C. V. Raman and K. S. Krishnan, Nature, 121(3048), 501, March 31, 1928

If we assume that the X-ray scattering of the 'unmodified' type observed by Prof. Compton corresponds to the normal or average state of the atoms and molecules, while the 'modified' scattering of altered wave-length corresponds to their fluctuations from that state, it would follow that we should expect also in the case of ordinary light two types of scattering, one determined by the normal optical properties of the atoms or molecules, and another representing the effect of their fluctuations from their normal state. It accordingly becomes necessary to test whether this is actually the case. The experiments we have made have confirmed this anticipation, and shown that in every case in which light is scattered by the molecules in dust-free liquids or gases, the diffuse radiation of the ordinary kind, having the same wave-length as the incident beam, is accompanied by a modified scattered radiation of degraded frequency.

The Raman Effect and Normal Raman Scattering

When light is scattered from a molecule most photons are elastically scattered. The scattered photons have the same energy (frequency) and, therefore, wavelength, as the incident photons. However, a small fraction of light (approximately 1 in 107 photons) is scattered at optical frequencies different from, and usually lower than, the frequency of the incident photons. The process leading to this inelastic scatter is the termed the Raman effect. Raman scattering can occur with a change in vibrational, rotational or electronic energy of a molecule. Chemists are concerned primarily with the vibrational Raman effect. We will use the term Raman effect to mean vibrational Raman effect only.


The difference in energy between the incident photon and the Raman scattered photon is equal to the energy of a vibration of the scattering molecule. A plot of intensity of scattered light versus energy difference is a Raman spectrum.

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