Raman Effect In Solids
Muhammad Umar Farooq
Dr. Muhammad Saeed Akhtar
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.
When light interacts with molecules of solid, the vast
majority of the photons are dispersed or scattered at
the same energy as the incident photons. This is
described as elastic scattering, or Rayleigh scattering.
CCl4 is a tetrahedral molecule with three pronounced Raman
active vibrational modes.
In the center of the spectrum is the Rayleigh scatter peak at
the laser wavelength. This peak is millions of times more
intense than the Raman scatter and is therefore normally
blocked by a notch or edge filter in the Raman spectrometer
but was included here for clarity.
Raman Spectrum of electron:
Inelastic scattering means that the energy of the emitted
photon is of either lower or higher energy than the incident
photon. After the scattering event, the sample is in a
different rotational or vibrational state.
This excitation puts the molecule into a virtual energy state for
a short time before the photon is emitted.
•Only those rotational transitions are allowed for
which ∆j=0 or ∆j= ±2
• When ∆j=0 scattered raman radiations will be same
• When ∆j= +2 gives stokes lines and ∆j= -2 gives anti-
• Raman spectroscopy is used to identify molecules and
study chemical bonding and intramolecular bonds.
• Raman spectroscopy is used to characterize materials
and find the crystallographic orientation of a sample.
• Detection of molecular impurities and additives.
• Determine molecular composition of surfaces.
Characteristics of Raman Spectrum:
• Intensity of stokes line is always greater than anti-
• Raman shift generally lies within the far and near
• Raman lines are symmetrically displaced about
• Raman lines are due to change in polarization of the
As per this concept when light travels through a fluid then
there is an interaction between light and fluid which is called
dispersion of light. Raman effect helps in explaining various
natural phenomenon on. like appearance of blue sky,
advanced sunrise and delayed sunset, etc. It also explains the
appearance of red sky during sunrise and sunset.