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Raman Spectroscopy
Introduction
• The Raman Effect is a phenomenon where light interacts with molecules and gets scattered.
• While most photons are scattered without any change in energy (this is called Rayleigh scattering), a very small number—about 1 in 10 million—are scattered with a change in energy.
• This is known as inelastic scattering.
• This effect discovered by Sir C.V. Raman in 1928.
• This effect involves a shift in the frequency of the scattered light.
• The new frequencies can be either lower (Stokes lines) or higher (anti-Stokes lines) than the original light.
• These changes in frequency correspond to the vibrational or rotational energy levels of the molecules, and the resulting spectrum is called the Raman spectrum.
• The difference between the original and scattered frequencies is called the Raman shift.
• This discovery is important because it provides a way to study the internal structure and energy levels of molecules.
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1. What is the Raman Effect?
The Raman Effect is a phenomenon where light interacts with molecules and gets scattered. In some rare cases, the scattered light has a different frequency from the incident light due to a change in energy, which is known as inelastic scattering.
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2. Who discovered the Raman Effect and in which year?
The Raman Effect was discovered by Sir C.V. Raman in the year 1928.
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3. What is Rayleigh scattering?
Rayleigh scattering is the elastic scattering of photons by molecules, where the scattered light has the same frequency (and energy) as the incident light.
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4. What is inelastic scattering of light?
Inelastic scattering of light occurs when photons are scattered with a change in energy, resulting in a different frequency than the incident light.
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5. What are Stokes lines in the Raman spectrum?
Stokes lines are the spectral lines on the lower frequency side of the Rayleigh line, produced when scattered photons lose energy.
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6. What are anti-Stokes lines?
Anti-Stokes lines are the spectral lines on the higher frequency side of the Rayleigh line, produced when scattered photons gain energy.
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7. Define Raman shift.
Raman shift is the difference in frequency between the incident light and the scattered light, and it corresponds to the vibrational or rotational energy levels of the molecules.
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8. How is the Raman Effect different from Rayleigh scattering?
In Rayleigh scattering, photons are scattered without any change in energy (elastic), whereas in the Raman Effect, a small fraction of photons are scattered with a change in energy (inelastic), resulting in frequency shifts.
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9. What type of molecular information can be obtained using the Raman Effect?
The Raman Effect provides information about the vibrational and rotational energy levels of molecules, which helps in understanding their internal structure.
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10. What causes the frequency shift in Raman scattering?
The frequency shift in Raman scattering is caused by the interaction of photons with the vibrational or rotational energy levels of molecules during inelastic scattering.