Raman Spectroscopy by Jivan Pund

1. RAMAN SPECTROSCOPY
Preparedby:Mr.JivanR.Pund
Guide: prof.Prof.PramodBurkale
Dr.Rajendragodecollegeof pharmacy,malkapur.

2. Sir Chandrasekhara Venkata
Raman
• November 7, 1888 - November 21,
1970
• Won the Nobel prize in 1930 for Physics
• Discovered the “Raman effect”
• Besides discovering the Raman effect he
• studied extensively in X-ray
Diffractions.
• phenomenon

3. CONTENT………
 INTRODUCTION
 PRINCIPLE
 QUANTUM MECHANISM OF R.S.
 INSTRUMENTATION
 DIFFERENCE
 ADVANTAGES/DISADVANTAGES
 APPLICATION

4. Introduction
 Raman spectroscopy deals with the scattering of light and not with its
absorption,homonuclear diatomic molecules such as H2 ,O2,N2 Etc.
 Which do not show I.R. spectra since they do not posses a permanent
dipole movement do show raman spectra since there vibration is
accompanied by change polarizability of the molecules.
 It gives imformation about molecular vibration that are inactive in the
infrared region bcz molecular symmetry
 When a substance (in any state) irradiated with monochromatic light or
photon of definite frequency light are scattered at right angle to the
incident light
 The frequency of scattered light is simillar to incident light and somim it
may lower or higher the frequency than the incident light it is to be
known as raman scattering
 Raman spectroscopy has another advantages in that is uses visible or
ultra violet radiation rather than I.R.radiation

5.  Stoke line: The frequency of scattered light is
lower than the incident light is know as the
stoke line
 Antistoke line : The frequiency of scattered light
is greater than incident light is known as anti-
stoke line
 Raileigh scattering: The frequency of incident
light is equil to scattered light is known as
raileigh scattering

6. ‘Principle’
 When light is incident on sample ,the molecules are absorb the light
and it may gives collisions of molecules
 There are lot of molecules and most of collision are identical that
means the freq. of incident light is equel to the scattering light
 But there is some molecule which have other frequency that means
there are may be greater than the incident light or less than the
incidernt light
 Raman Scattering
 a

8. Quantum Theory of Raman Scattering
v0 > vs v0 = vs v0 < vs
 = v0 - vs  =0  = v0 + vs

9. INSTRUMENTATION
Instrumentation for modern Raman spectroscopy consists of three
components:
A laser source, a sample illumination system and a suitable
spectrometer.
1. Source
2. Sample Illumination System
3. Raman Spectrometers
Source
The sources used in modern Raman spectrometry are nearly
always lasers because their high intensity is necessary to produce
Raman scattering of sufficient intensity to be measured with a
reasonable signal-to-noise ratio. Because the intensity of Raman
scattering varies as the fourth power of the frequency, argon and
krypton ion sources that emit in the blue and green region of the
spectrum have and advantage over the other sources.

11. Sample Illumination System
Liquid Samples: A major advantage of sample handling in Raman
spectroscopy compared with infrared arises because water is a
weak Raman scatterer but a strong absorber of infrared radiation.
Thus, aqueous solutions can be studied by Raman spectroscopy but
not by infrared. This advantage is particularly important for
biological and inorganic systems and in studies dealing with water
pollution problems.
Solid Samples: Raman spectra of solid samples are often acquired
by filling a small cavity with the sample after it has been ground
to a fine powder. Polymers can usually be examined directly with
no sample pretreatment.
Gas sample:Gas are normally contain glass tubes 1-2 cm diameter
and about1mm in thick.Gases can also be sealed in capillary tubes.

12. Raman Spectrometers
Raman spectrometers were similar in design and used
the same type of components as the classical
ultraviolet/visible dispersing instruments.
Most employed double grating systems to minimize the
spurious radiation reaching the transducer.
Photomultipliers served as transducers.
Grating used in raman spectroscopy.
Typical grating used for R.S.vary from 300 groove/mm(low
resolution)through 1800 groove/mm (high resolution)

14.  DETECTOR FOR RAMAN SPCTROSCOPY
 1.Single channel detector
1.Photodiode
2.Photomultiplier tubes

15. Raman vs IR Spectra

16. Difference between IR & Raman
spectroscopy
IR
 It is the result of absorption of
light by vibrating molecule.
 The presence of permanent
dipole moment in a molecule
may be regarded as a critereon
of IR spectra.
 It requires at least two separate
runs.
 Water cannot be used as a
solvent.
 Method is accurate& sensitive
Raman
 It is the result of Scattering of light
by vibrating molecule.
 Polarizability of the molecule will
decide whether the raman spectra
will be observed or not.
 It can be recorded in only one
exposure.
 Water can be used as a solvent
 Method is very accurate but is not
very sensitive

17.  Optical systems are made up of
special crystals such as CaF2,NaBr,
NaCl etc.
 Generally dilute solutions are
preffered.
 Homonuclear diatomic molecules
are not found tobe IR active.
 Optical systems are made up of
glass or quartz.
 Raman lines are weeker in
intensity so concentrated solutions
are preffered.
 Homonuclear diatomic molecules
are found tobe active.

18. Advantages
 Water can be used as solvent.
 Very suitable for biological sample
 Glass and quartz ,lenses,cells and optical fibers can be used
 Standard detecrtor used
Disadvantages
 Complicated and costly equiupments
 Not suitable for vibrations of bond with very ;low polarizability

19. Application
 Elucidation of molecular structure
 Biological Applications of Raman Spectroscopy
 Study ionic equilibria
 Study of hydrogen bonded equilibria
 Qualitatve analysis (identification)
 Quantitative analysis (estmation)