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Cabannes and Rocard: Explication of the Raman Effect


The Raman Effect
Edward Teller Scientist
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Now, all this means nothing if I tell it to you this way. It may begin to mean something if I give you some examples. One of these examples is the Raman Effect. Raman, a Hindu, discovered that when molecules scatter light, the frequency of light is essentially unchanged. But, in addition to that unchanged frequency, there are weaker frequencies in the scattering. In comes a frequency of light, the frequency is connected with the energy; the higher the frequency, the higher the energy. Most frequently, the light will come out with the same frequency. But sometimes, the light will come out with less energy and less frequency, enough frequency and enough energy just to excite one quantum of the vibration of the molecule. In quantum mechanics, that's very simple. What happens in classical theory? And the simplicity is really changed into something complex. When you do not talk about a simple diatomic molecule like nitrogen having two nuclei that vibrate against each other. Instead, take benzene: six carbons and six hydrogens. Take carbon tetrachloride: one carbon atom and two- and four chlorines around it. There are many vibrations that this molecule can execute. And some of them will appear in the Raman effect, some vibrations can retain a part of the energy that have come in, and some not. This is governed by what are called, obviously, selection rules. How do we explain these selection rules? In quantum mechanics it's straight forward but a little involved.

The late Hungarian-American physicist Edward Teller helped to develop the atomic bomb and provided the theoretical framework for the hydrogen bomb. During his long and sometimes controversial career he was a staunch advocate of nuclear power and also of a strong defence policy, calling for the development of advanced thermonuclear weapons.

Listeners: John H. Nuckolls

John H. Nuckolls was Director of the Lawrence Livermore National Laboratory from 1988 to 1994. He joined the Laboratory in 1955, 3 years after its establishment, with a masters degree in physics from Columbia. He rose to become the Laboratory's Associate Director for Physics before his appointment as Director in 1988.

Nuckolls, a laser fusion and nuclear weapons physicist, helped pioneer the use of computers to understand and simulate physics phenomena at extremes of temperature, density and short time scales. He is internationally recognised for his work in the development and control of nuclear explosions and as a pioneer in the development of laser fusion.

Duration: 3 minutes, 13 seconds

Date story recorded: June 1996

Date story went live: 24 January 2008