What is Raman spectroscopy and how it works?
Raman spectroscopy belongs into the category of vibrational spectroscopy. This means that it analyzes a sample chemically, by using light to create (excite) molecular vibration, and interpreting this interaction afterwards. It is based on the inelastic scattering of light that occurs when matter is irradiated by light.
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.
Which radiation is used in Raman spectroscopy?
Infrared beams are used for illumination of the molecules and the dispersed light if collected on the detector.
What is Raman effect formula?
By further investigating the quantum interpretation of the Raman effect, it can be shown that the power of the scattered light, Ps, is equal to the product of the intensity of the incident photons, Io, and a value known as the Raman cross-section, σR. It can be shown that, Equation R-9.
What is the selection rule of Raman spectra?
The selection rule says, that vibrations are only IR active (or allowed), if the molecular dipole moment changes during the vibration. A diatomic molecule with the same atoms cannot be excited to vibrate because no dipole moment is present.
Why laser is used in Raman spectroscopy?
In modern Raman spectrometers (Fig. 2.1), lasers are used as a photon source due to their highly monochromatic nature, and high beam fluxes. This is necessary as the Raman effect is weak, typically the Stokes lines are ~105 times weaker than the Rayleigh scattered component.
What is the sensitivity of Raman spectroscopy?
Raman testing sensitivity was calculated to be 98% and specificity was 100%.
What is Raman effect example?
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.
Why is the sea blue in Colour According to Raman?
He immediately began to conduct experiments on board the ship using some simple instruments he had with him. At that time, scientists believed the sea was blue because it reflected the colour of the sky, but Raman found that it was the water itself that caused blue light to scatter more than other colours in light.
What is the difference between IR and Raman spectroscopy?
Raman spectroscopy depends on a change in polarizability of a molecule, whereas IR spectroscopy depends on a change in the dipole moment. Raman spectroscopy measures relative frequencies at which a sample scatters radiation, unlike IR spectroscopy which measures absolute frequencies at which a sample absorbs radiation.
What are Raman active molecules?
Raman spectroscopy occurs as a result of a molecular vibration causing a “change in polarizability” of the molecule. In contrast, for a molecule to be infrared active, the vibration must cause a change in the permanent dipole moment. A simple case of a Raman Active molecule would be a species such as CS2.
What is the wavelength of Raman spectroscopy?
The most commonly used laser wavelength in Raman spectroscopy is 785 nm which offers low fluorescence whilst retaining relatively high Raman intensity. However, for samples which suffer from large fluorescence backgrounds, such as dyes, a 1064 nm laser may be needed.
What are the types of Raman?
There are now more than 25 different types of known Raman spectroscopy techniques, such as spontaneous Raman, hyper-Raman scattering, Fourier transform Raman scattering [5], Raman-induced Kerr effect spectroscopy [6] and stimulated/coherent Raman scattering [1].
Who invented Raman Spectroscopy?
Sir C.V. Raman
Sir C.V. Raman with the quartz spectrograph used to measure the wavelengths of the scattered light that became known as the Raman Effect.
What is Raman effect in simple words?