Raman Effect / Natonal Science Day , 28 February , Q&A

Introduction :

When a beam of monochromatic light (radiation) is allowed to pass through a transparent medium (solid, dust-free liquids and gasses), a fraction of the incident (incoming) radiation gets scattered. Most of the scattered radiations have the same frequency as the incident one. But few are scattered with a difference in frequency. This type of scattering, first observed in liquids by the Indian Physicist C V Raman in 1928, is known as Raman Effect or Raman Scattering.

 Definition : 

This is a phenomenon in spectroscopy i.e., change in the wavelength of light that occurs when a light beam is deflected by molecules. When a beam of light traverses a dust-free, transparent sample of a chemical compound, a small fraction of the light emerges in directions other than that of the incident (incoming) beam. Most of the scattered light is of unchanged wavelength. A small part, however, has wavelengths different from the wavelength of the incident light, its presence is a result of the Raman Effect.

History :

This remarkable history began when an Indian Scientist (Physicist) C V Raman studying about "Molecular Diffraction  of Light " and in 1922 he published his work on the "Molecular Diffraction Of Light", the first of a series of investigation with his collaborates that ultimately led to his discovery (on 28 February 1928) of the radiation effect that bears his name . The Raman Effect was first reported by C V Raman and his Student K S Krishnan.   

Raman received the Nobel Prize in 1930 for his great contribution on the scattering of light. In that time C V Raman and his student Krishnan used a mercury lamp and photographic plats to record spectra while studying about "Molecular Diffraction Of Light".

Although in modern civilization LASER sources have revolutionized the technique of studying the Raman Effect. As a Raman source, LASER is ideal having some advantages like as following :

  1) it gives an extremely narrow and highly monochromatic beam of light, 

  2) it can thus be focused finely into a small sample and

  3) a fairly large power (many mW to few Watts) may be concentrated onto the sample.se

In 1998 the Raman Effect was designated a National Historic Chemical Landmark by the American Chemical Society in recognition of its significance as a tool for analyzing the composition of liquids, gasses, and solids.

We are very thankful to prof. CV Raman for his great contribution and give us a remarkable theory about "Molecular Diffraction Of Light" and help us to find out the reason behind blue sky. 

Why the Raman Effect Is So Important? / Applications Of Raman Effect :

Raman effect confirms the molecular structure in gases, liquids and solids states. For non-polar homo-nuclear molecules H2, O2, N2 etc no infrared rotation-vibration spectra are observed. Raman Effect also helps us to classify substances according to their molecular structure. After getting Raman Effect we are able to successfully explain the mystery of blue sky i.e., the reason behind the sky looks blue.

National Science Day, 28 February :

After giving his remarkable theory, in 1986, The National Council For Science and Technology Communication (NCSTC) asked, the Government of India to designate February 28 as National Science Day (NSD) in India to mark the discovery of Raman Effect. The event NSD is now celebrated all over the country and is celebrated every year on 28 February in school, colleges, universities and other academic, scientific, technical, medical and research institutions. The celebration also includes public speeches, radio, TV, science movies, science exhibitions based on themes and concepts, watching the night sky, live project, research demonstration, debates, quiz competitions, lectures, science model exhibitions and many more activities. On the occasion of the first National Science Day, NCSTC announced Popularization awards for recognizing outstanding effort in the area of Science Communication and Popularization.