Indian physicist Chandrasekhara Venkata Raman discovered how the scattering of light by gas, liquid, or solid molecules causes a change in the wavelength of light—an effect known as Raman scattering. The resulting spectra, called Raman spectroscopy, which emerged from this scattering, are used in the identification and analysis of the structures of molecules. With this discovery, Raman received the title of knight and became the first Asian to win the Nobel Prize in 1930.
Who Was Chandrasekhara Venkata Raman?
Chandrasekhara Venkata Raman was born in the village of Thiruvanaikaval near Tiruchirappalli in Tamil Nadu, a southern Indian province. Her father, Chandrasekhara Iyer, was a professor of physics and mathematics. Raman went to Presidency College in Madras for graduate education. His first research was published here; his article on optics, “Unsymmetrical Diffraction,” appeared in the British Philosophical Magazine. In colonial times, it was not possible to pursue a scientific research career in India without graduating from British universities.
Thus, Raman took the highly demanded Indian Government Financial Audit and Accounting Exams and came first in them. In 1907, he was appointed an assistant general accountant and worked as an accountant in Calcutta for 10 years. Shortly after he arrived in Calcutta, he came across the Indian Association for the Cultivation of Science, which was established for Mahendralal Sircar. Despite the limited possibilities of society, Raman started to work here in his spare time. In his first prominent work, he expanded the definition of the fundamental vibration modes (previously proposed by Hermann von Helmholtz) into more complex modes.
Chandrasekhara Venkata Raman’s work in the community caught the attention of Sir Ashutosh Mukherjee, the founder of the University of Calcutta, who offered him the post of Palit Professor of Physics. Raman accepted this offer in 1917, which meant he would have to leave the well-paying civil service and take a big pay cut.
Raman made his first trip abroad to England in 1921, when he participated in a scientific conference attended by representatives from universities in the British Empire. While returning to India by sea, the intense blue color of the Mediterranean attracted his attention. Physicist Lord Rayleigh explained this event as the reflection of the blue color in the sky over the sea as a result of the elastic scattering of the sunlight (Rayleigh scattering) in the atmosphere. But looking at the sea surface through a light-polarizing tool called a “Nicol prism” at a 53-degree angle (called a “Brewster angle”) showed that this wasn’t enough.
After the experiments conducted in Calcutta, C. V. Raman concluded that the blue color of the water comes from the light emitted by the water molecules, just as the blue color of the sky originates from the scattering of the sunlight emitted by the air molecules. In 1922, this discovery appeared in Raman’s small book, “Molecular Diffraction of Light,” ultimately leading to intense experimentation and the discovery of the famous effect bearing his name.
Shedding light on scattered light
C.V. Raman scattering was first noticed in Raman’s lab around 1923 and was published in the periodical Indian Journal of Physics, which Raman founded in 1928. In addition to the primary Rayleigh scattering components that have the same frequency as the incident light, Raman also saw that there is a weaker secondary component with a variable frequency (i.e., energy level).
Initially, Raman scattering was thought to be due to fluorescence, but Raman eliminated this possibility by showing that the scattered light was highly polarized in the experiments conducted with K.S. Krishnan. Raman realized that the second beam he saw at the beginning of 1928 was the same thing as an X-ray. This was the Compton scattering, which Arthur Compton discovered in 1923. This happens when X-rays pass through a substance and are scattered, making the wavelength longer.
Under the Compton effect, X-ray radiation behaves like quantized particles (photons) that enter into an elastic collision with the electrons in the substance. This effect was determining evidence of the presence of such quantities that are proportional to their frequency of energy and momentum. In Raman scattering, visible light acts as quantized particles that enter into an inelastic collision with the molecules. Raman scattering has either a lower or higher frequency than the radiation that it interacts with, depending on whether the light quantum energizes the molecule or absorbs energy from it. The theory was envisioned by Werner Heisenberg and Hendrik Kramers in their studies on the quantum theory of scattering in 1925. The Raman scattering thus provided strong evidence of the quantized nature of light.
The main significance of the Raman effect was that it provided a powerful technique that allowed the study of molecular structures and energy levels. In the Raman spectrum, the shift in frequency between interacting radiation and secondary radiation is directly related to the difference between initial and final molecular energy levels, and therefore Raman scattering can be used to detect certain molecules and chemical bonds. The first information gathered mostly includes the rotation and vibration levels of the molecules. These were previously available only on the infrared spectrum and were difficult to obtain. Raman spectroscopy has made this type of information more affordable and available.
Other achievements of Chandrasekhara Venkata Raman
With the discovery of the laser in the 1960s, Raman spectroscopy was further developed and finalized. This enabled the technique to be used in microscopic examinations and measurements of the substance. Today, it is used for many different things in many different fields, such as real-time monitoring of anesthetic gas during surgery, protecting historical monuments, and detecting drugs, explosives, and forensic trace evidence by law enforcement and security services.
In 1933, Chandrasekhara Venkata Raman left Calcutta to join the Indian Institute of Science in Bangalore as the first Indian executive. He trained a large number of students who served in important positions in both Calcutta and Bangalore. Although he left the management position four years later, he continued to teach as a physics professor until his retirement in 1948. After retirement, he founded the Raman Research Institute, where he worked on the optics of minerals and the physiology of vision. His most important contribution to this time is the Raman-Nath theory of how light is bent by ultrasonic waves.
In the 1940s, Raman studied Max Cage and Born-Van Karman’s theory of lattice vibrations. This theory predicted partial continuity for the Raman spectrum, but Raman found significant distinct features in the spectrum of the diamond. The solution to this dispute was provided by other scientists in 1953: the discrete features observed were attributed to singularities that exist in some of the normal modes in partial continuity.
Chandrasekhara Venkata Raman was a true nature lover. Whether it was the color of the sea or the minerals, the beauty of nature fascinated him. He was pleased by the sound, which led him to work on musical instruments and in domes with good acoustics where whispers are heard from everywhere. By studying physics, he celebrated nature’s beauty with his science.
Bibliography:
- “Raman effect” Archived 24 October 2018 at the Wayback Machine. Collins English Dictionary.
- Bhagavantam, Suri (1971). “Chandrasekhara Venkata Raman, 1888-1970”. Biographical Memoirs of Fellows of the Royal Society. 17: 564–592. doi:10.1098/rsbm.1971.0022.
- “CV RAMAN: A Creative Mind Par Excellence”. Hindustan Times. 8 July 2019.
- Jayaraman, Aiyasami (1989). Chandrasekhara Venkata Raman: A Memoir. Bengaluru: Indian Academy of Sciences. p. 4. ISBN 978-81-85336-24-4.
