Context: 28th February is celebrated as the National Science Day in India to mark the discovery of Raman Effect by CV Raman on 28th February 1928. C V Raman was endowed with the Nobel Prize in Physics in 1930 for discovering the Raman Effect.
Raman Effect
If you have seen the photographs of moon, you might have noticed that the sky looks black where earth’s sky looks blue.
Similar question aroused in the mind of CV Raman. It was while returning from England abroad a ship that Raman found himself facing a question that left him perplexed. “A glass of water does not have any colour of its own. But the same water in the deep sea appears a brilliant blue. Why is this so?”, he asked himself as he gazed out at the azure waters of the Mediterranean Sea.
What he found was that the sea looks blue for pretty much the same reason the sky looks blue — the water was causing blue light to scatter more than other colours in the light. Excited by this realization, Raman wrote to Nature (a premier science journal) as soon as he arrived in India.
Raman effect, 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 this scattered light is of unchanged wavelength. A small part, however, has wavelengths different from that of the incident light; its presence is a result of the Raman effect.
In order to understand Raman Effect, first lets understand the scattering phenomenon.
- When sunlight enters the atmosphere of the earth, the atoms and molecules of different gasses present in the air absorb the light. Then these atoms re-emit light in all directions. This process is known as Scattering of light.
The scattered light can be:
- Elastic (Rayleigh Scattering), the energy released is at the same frequency as that of the incident radiation; or
- Inelastic (Raman Scattering), the energy release is at a higher or lower frequency than that of the incident radiation.
Raman Scattering Process
- The Raman scattering process, as described by quantum mechanics, is when photons interact with a molecule, and the molecule may be advanced to a higher energy, virtual state. From this higher energy state, there may be a few different outcomes. One such outcome would be that the molecule relaxes to a vibrational energy level that is different than that of its beginning state producing a photon of different energy. The difference between the energy of the incident photon and the energy of the scattered photon is called the Raman shift.
Applications of Raman effect:
Raman spectroscopy is a highly potent tool as it offers a non-destructive, highly informative approach for analyzing the molecular compositions and structures of a wide range of materials. Its versatility and applicability across various scientific disciplines make it a valuable tool for researchers, scientists, and industrial professionals alike. Examples of Raman spectroscopy’s applications include:
- Explanation of Blue ocean: Water molecules scatter light just like air molecules do. Light scattering in air was Rayleigh’s explanation for why the sky was blue; and Raman found that this was true also for why the sea was blue.
- Material Science: Raman spectroscopy is utilized for material characterization, identification of polymorphs, detection of impurities, and analysis of crystal structures.
- Pharmaceutical Analysis: Raman spectroscopy plays a vital role in pharmaceutical research and quality control. It enables the identification of active ingredients, detection of counterfeit drugs, and analysis of drug delivery systems.
- Forensic Science: Raman spectroscopy assists forensic scientists in identifying and characterizing trace evidence, such as fibers, paints, and drugs.
- Environmental Monitoring: Raman spectroscopy is employed for environmental analysis, including the identification and quantification of pollutants, monitoring of water quality, and analysis of atmospheric particulates.