describe both quantum and classical theory of a raman effect
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Quantum theory
When light interacts with matter, the photons which make up the light may be absorbed or scattered, or may not interact with the material and may pass straight through it (Smith and Dent, 2005). When monochromatic light interacts with molecules, most of the photons are scattered without any change in energy. This process is called elastic or Rayleigh scattering, and it occurs when the electrons in a molecule oscillate in resonance with the applied electric field of the incident light. However, a small number of photons (1 out of 106 to 109) are inelastically scattered and undergo a change in energy.
The inelastic scattering process is called Raman scattering (Raman effect). The change in photon energy occurs because a molecule may vibrate during the time the electrons oscillate in resonance with the applied electric field. A vibrational mode that changes molecular polarizability (dipole moment induced by electric field) results in a change of incident photon energy. The difference in energy between the incident photons and inelastically scattered photons is called Raman shift. A plot of the intensity of the inelastically scattered light as a function of the energy change is called Raman spectrum.
Classical theory
The classical theory of the Raman effect is based upon polarizability of molecules, which reflects how easy an electron cloud of a molecule can be distorted by an electric field (light).
The technique is based on molecular deformations in electric field E determined by molecular polarizability α. The laser beam can be considered as an oscillating electromagnetic wave with electrical vector E. Upon interaction with the sample it induces electric dipole moment P = αE which deforms molecules. Because of periodical deformation, molecules start vibrating with characteristic frequency (McCreery, 2000).
The scattered light can have a frequency equal to the incident light (Rayleigh), equal to the incident light minus the vibrational frequency (Stokes) and equal to the incident light plus the vibrational frequency (anti-Stokes).
When light interacts with matter, the photons which make up the light may be absorbed or scattered, or may not interact with the material and may pass straight through it (Smith and Dent, 2005). When monochromatic light interacts with molecules, most of the photons are scattered without any change in energy. This process is called elastic or Rayleigh scattering, and it occurs when the electrons in a molecule oscillate in resonance with the applied electric field of the incident light. However, a small number of photons (1 out of 106 to 109) are inelastically scattered and undergo a change in energy.
The inelastic scattering process is called Raman scattering (Raman effect). The change in photon energy occurs because a molecule may vibrate during the time the electrons oscillate in resonance with the applied electric field. A vibrational mode that changes molecular polarizability (dipole moment induced by electric field) results in a change of incident photon energy. The difference in energy between the incident photons and inelastically scattered photons is called Raman shift. A plot of the intensity of the inelastically scattered light as a function of the energy change is called Raman spectrum.
Classical theory
The classical theory of the Raman effect is based upon polarizability of molecules, which reflects how easy an electron cloud of a molecule can be distorted by an electric field (light).
The technique is based on molecular deformations in electric field E determined by molecular polarizability α. The laser beam can be considered as an oscillating electromagnetic wave with electrical vector E. Upon interaction with the sample it induces electric dipole moment P = αE which deforms molecules. Because of periodical deformation, molecules start vibrating with characteristic frequency (McCreery, 2000).
The scattered light can have a frequency equal to the incident light (Rayleigh), equal to the incident light minus the vibrational frequency (Stokes) and equal to the incident light plus the vibrational frequency (anti-Stokes).
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