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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.
Sir C. V. Raman
Chandrasekhara Venkata Raman was born at Trichy in Tamilnadu in south India on November 7th, 1888. He entered Presidency College, Madras, in 1902, and in 1904 passed his B.A. examination, winning the first place and the gold medal in physics; in 1907 he gained his M.A. degree, obtaining the highest distinctions. In 1922 he published his work on the "Molecular Diffraction of Light," the first of a series of investigations with his collaborators which ultimately led to his discovery of the radiation effect, on the 28th of February, 1928, which bears his name ("A new radiation", Indian J. Phys., 2 (1928) 387), and which gained him the 1930 Nobel Prize in Physics. In 1934, Raman became the director of the newly established Indian Institute of Science in Bangalore, where two years later he continued as a professor of physics. In 1947, he was appointed as the first National Professor by the new government of Independent India. He retired from the Indian Institute in 1948 and a year later he established the Raman Research Institute in Bangalore, serving as its director and remained active there until his death on November 21, 1970, at the age of eighty two.
The Classical Raman Effect
The distortion of a molecule in an electric field is determined by its polarisability .
The Raman Effect is used in materials analysis. The frequency of light scattered from a molecule may be changed based on the structural characteristics of the molecular bonds. A monochromatic light source (laser) is required for illumination, and a spectrogram of the scattered light then shows the deviations caused by state changes in the molecule.
- "Dynamical Theory of the Motion of Bowed Strings", Bulletin, Indian Association for the Advancement of Science, 1914
- "On the molecular scattering of light in water and the colour of the sea", Proceedings of the Royal Society, 1922
- "A new type of Secondary Radiation", Nature, 1928
- "A new radiation", Indian Journal of Physics, 1928
- Aspects of Science, 1948
- The New Physics: Talks on Aspects of Science, 1951
- Lectures on Physical Optics, 1959
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