RAMAN EFFECT

1. 1
SULTANPUR(U.P.)
DEPARTMENT OF physics
SESSION: 2016 -17
Submitted to:
H.O.D PHYSICS
KNIPSS SULTANPUR
Submitted By:
M.Sc. PRE. PHYSICS
KNIPSS SULTANPUR

9. Introduction :- Rayleigh observed that if a substance is
irradiated with mono chromatic Light, the scattered light
is observed in a direction at right angles to the incident
light. This is shown in fig.4.1

10. When a spectroscope was used to investigate the scattered Light, it
was found that the frequency of Scattered Light was same as the
frequency of the incident raditions. This phenomenon was observed
By rayleigh and is known as was observed by rayleigh and known
as Rayleigh Scattering.
In 1923 Smekel predicted theoretically that if a Substance in the
gaseous, liquid or solid state in irradiated with monochromatic light,
the scattered light should contain radiations with different
frequencies than the frequency of incident light.
Raman Effect :- In 1928 Sir C.V. Raman discovered that when a
beam of monochromatic light was allowed to pass through a
substance in the solid, liquid or gaseous state, the scattered Light
contains some additional frequencies over and over that of incident
frequency. This is Known as Raman Effect . and is a beautiful
confirmation of the smekels prediction.

11. The lines whose wave lengths have been modified in Rama effect are
called Raman lines. The lines having wave lengths greater than that of
incident wavelengths are stokes lines and those having shorter wave
lengths anti stokes lines and those having shorter wave lengths Anti-
stokes lines if Vi is frequency of incident radiation and Vs is the
radiation scattered by the giving Molecule species, then the Raman shift
∆V= Vi –Vs.
The Raman shift does not depend upon the frequency of incident light but it
is regarded as a characteristic of the Substance causing Raman effect. For
stokes line, ∆V is positive and for anti stokes lines ∆V is negative.(Fig.-
4.2&4.3)

13. Characteristic properties of Raman lines :-
The lines Observed in Raman effect exhibit a number of characteristic
which are Summarished as follows :
1. The intensity of stocks lines is always greater than the corresponding
anti stokes lines.
2. Raman shift ∆V generally lines within far and near infrared regions of
the spectrum It means that the Raman frequencies are generally
identical with the infrared vibrational Frequencies. (The small
difference can be attributed to experimental errors) it should be noted
that it is not necessary that all Raman lines will have their
corresponding infrared bands are similarly all infrared band’s may not
have the corresponding Raman Lines.
3. Raman Lines are symmetrically displaced about the parent lines when
the temperature rises, their individual separations from the parent
lines decrease.

14. 4. The frequency difference between the modified and parent
lines represent the frequency of the absorption band of the
material.
Physical Significance :- Since the Raman effect depends upon the
polarizability of the molecule it can be observed For molecules which
have no net dipole moment and therefore produce no pure rotational
spectrum this process can yield information about the moment of intra
and hence the structure of molecule.
In Roman effect an intense monochromatic light source give scattered
light which includes one or more “side bonds” that are offset by rational
and/or irrational energy difference .This is potentially very useful for
remote sensing. Since the sideband frequencies contain information
about the scattering medium which could be useful for identification.

15. In Raman effect water can be used as a solvent while in I.R. spectroscopy water
can not be used as a solvent because it is opaque to infrared radiation.
Application of Raman Spectra : The Raman effect is very important
because of its large number of applications. In fact it is an useful tool for solving
the intricate research problems concerning .The constitution of compounds. The
application of Raman effect are very much and ever increasing and therefore, it is
not possible to include all the applications. Some of its application are discussed
below.
1. All substances to be analyzed by Raman spectroscopy should be free from
impurities Likely To absorb in the range of Raman spectrum. Gas
chromatography or Vacuum distillation Can be used for purification of liquids.
Crystalline substances can be examined in solution as a melt in powered form or
as single crystals. Solvent are purified by distillation in grease free apparatus or
by filtration through alumina.