Table of Contents
What is quantum theory of Raman spectroscopy?
A system of coupled equations for the amplitudes of scattered photons and molecular vibrations are derived. The molecular vibration coordinates are then eliminated using the random phase approximation. The equations which result assume the form of coupled equations for the first Stokes and anti-Stokes lights.
What is Raman effect explain quantum theory of Raman effect?
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.
What is the mechanism behind Raman lines?
The Raman effect is based on the interaction between the electron cloud of a sample and the external electric field of the monochromatic light, which can create an induced dipole moment within the molecule based on its polarizability.
How will you explain Raman scattering by classical and quantum mechanical theories?
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.
Who proposed the quantum theory?
Neil Bohr, Max Plank and Albert Einstein are considered the founding fathers of quantum theory. Neil Bohr and Max Plank received the Nobel Prize for their work on quanta. The origin of quantum theory can be traced back to 1900 when German physicist Max Plank published the effect of radiation on a black body.
What is the first postulate of quantum mechanics?
First postulate of Quantum mechanics: Every physically-realizable state of the system is described in quantum mechanics by a state function ψ that contains all accessible physical information about the system in that state.
What are the two methods of excitation of the samples in Raman Spectroscopy?
(ii) During our experiment, we used mostly two different excitation sources: Diode laser with wavelength at 782 nm and Argon-Ion laser with excitation wavelength at 514.5 nm.
What are Stokes and Antistokes lines in Raman spectrum?
Stokes lines are of longer wavelength than that of the exciting radiation responsible for the fluorescence or Raman effect. Anti-Stokes lines are found in fluorescence and in Raman spectra when the atoms or molecules of the material are already in an excited state (as when at high temperature).
What is Raman scattering cross section?
A typical cross-section for Raman scatter is 10-30 cm2 sr-1. Again the exact value will depend upon the excitation frequency and distance from the absorption band.
Is Raman scattering directional?
Inelastic scatter, such as Raman, absorbs sufficient energy to promote a rotational or vibrational transition. The remaining energy is scattered as a lower energy photon. Scattered light has a directional probability with the shape of a torus. The torus axis is in the direction of the electric vector.
What is the effect of Raman scattering?
The second effect is the Raman scattered component and when expanded to, can be shown to shift the frequency of the incident light by plus or minus the frequency of the molecular vibration.
What is Rayleigh scatter and Raman scatter of photons?
The elastically scattered photons are referred to as Rayleigh scatter and have no analytical value. The inelastically scattered photons are referred to as Raman scatter.
What is the difference between single photon event and Raman event?
This is a single photon event with respect to the molecule’s dipole moment. In contrast, Raman scattering, or the Raman effect, is a two-photon event involving the change in polarizability of the molecule with respect to its vibrational motion in the form of scattered energy.
What is coherent anti-Stokes Raman scattering (CARS)?
Coherent anti-Stokes Raman scattering (CARS) is based on a nonlinear mixing process of multiple lasers that is used to enhance the weak (spontaneous) Raman signal. In the CARS process a pump laser beam and a Stokes laser beam interact, producing an anti-Stokes signal at a certain frequency.