Can Raman shift be negative?
The peaks in the spectrum with negative Raman shift are known as anti-Stokes lines.
Why it is called Raman shift?
It is named after the Indian physicist C. V. Raman who, together with his research partner K. S. Krishnan, was the first to observe Raman scattering in 1928.
What does Raman shift depend on?
Raman shift depends on molecular energy level of the scatterer. Different molecular energy levels produce different Raman shift for same incident wavelength.
What is meant by 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 are Stokes and anti Stokes 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).
Why is Raman scattering weak?
This occurs because only molecules that are vibrationally excited prior to irradiation can give rise to the anti-Stokes line. Hence, in Raman spectroscopy, only the more intense Stokes line is normally measured – Raman scattering is a relatively weak process. The number of photons Raman scattered is quite small.
What is Stokes and anti-Stokes lines?
Stokes lines are of longer wavelength than that of the exciting radiation responsible for the fluorescence or Raman effect. Thus, anti-Stokes lines are always of shorter wavelength than that of the light that produces them.
Which are Raman lines?
The Raman lines in the scattered light are weaker than the light at the original wavelength. The Raman-shifted lines occur both at longer and shorter wavelengths than the original light; the lines at the shorter wavelengths are usually very weak. The Raman spectrum is characteristic of the scattering molecule.
Which type of scattering is strongest?
Another finding is that forward scattering is stronger than backward scattering, because the relative phase differences of contributions from different scattering locations on the particles become smaller.
How does Raman scattering of monochromatic light work?
Raman spectroscopy. It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range. The laser light interacts with molecular vibrations, phonons or other excitations in the system, resulting in the energy of the laser photons being shifted up or down.
Why is Stokes Raman scattering an inelastic process?
Stokes Raman scattering is the inelastic scattering process that transfers energy from the light to a vibration of the molecule. Therefore, the scattered photon has lower energy and a higher wavelength than the incident photon.
How are the Raman and Rayleigh effects described?
Copyright © 1997 Encyclopædia Britannica, Inc Raman scattering •Classically, the Raman and Rayleigh effects can be described by the polarizability of a moleculedescribed by the polarizability of a molecule •The induced dipoleThe induced dipole can be writtencan be written = E; (1)
How to calculate the Raman shift of oxygen?
Calculate the oxygen Raman wavelength: According to the Table the Raman shift is 1556 cm-1. With an excitation wavelength at 532 nm the oxygen Stokes line will appear at 1/532 nm – 1556 cm-1 = 18797 cm-1– 1556 cm-1= 17241 cm-1= 580 nm