Raman Spectroscopy

1. Presented by-
Name- Jubair Sikdar
Roll no-04
M. Pharm 1st semester
Department of Pharmaceutical Chemistry
RAMAN SPECTROSCOPY
NETES Institute of Pharmaceutical Sciences, Mirza

2. CONTENTS
 INTRODUCTION
 PRINCIPLE
 INSTRUMENTATION
 APPLICATION

3. INTRODUCATION
 Raman spectroscopy is a technique for studying molecular vibrations by
light scattering.
 Raman spectroscopy was discovered by C. V. Raman in 1928.
 Raman spectroscopy deals with the scattering of light.
 It is a spectroscopic technique used to observe vibration, rotational and
other low-frequency modes in a system.
 Raman spectroscopy is commonly used in chemistry to provide a fingerprint
by which molecules can be identified.

4. PRINCIPLE
 When radiation from a source is passed through a sample, some of the
radiation is scattered by the molecules present. The beam of radiation is
merely dispersed in space.
 Three types of scattering occur. They are called Rayleigh scattering, Stokes
scattering, and anti-Stokes scattering.
 Rayleigh scattering occurs as a result of elastic collisions between the
photons and the molecules in the sample; no energy is lost on collision.
 Some of the photons are scattered with less energy after their interaction
with molecules and some photons are scattered with more energy. These
spectral lines are called Raman lines

5.  The Raman–Stokes lines are from those photons scattered with less energy
than the incident radiation; the Raman–anti-Stokes lines are from the photons
scattered with more energy.
 The differences in the energies of the scattered photons from the incident
photons have been found to correspond to vibrational transitions.
Figure: Shows the process of Rayleigh and Raman scattering.

6. INSTRUMENTATION
Instrumentation for modern Raman spectroscopy consists of three
component
•Light Source
•Samples and Sample Holders for Raman Spectroscopy
•Suitable Spectrometer
Figure: Idealized layout of a Raman spectrometer

7. Light Source:
Monochromatic light sources are required for Raman spectroscopy. The light
sources used originally were simple UV light sources, such as Hg arc lamps.
The Raman signal is directly proportional to the power of the light source.
Modern Raman instruments use a laser as the light source. Some common
Laser sourses for Raman spectroscopy are
Laser Type Wavelength, nm
Argon ion 488.0 or 514.5
Krypton ion 530 or 514
Hellium-neon 632.8
Diode 785 or 830
Nd-YAG 1064

8. Samples and Sample Holders for Raman Spectroscopy:
 Because the laser light source can be focused to a small spot, very small
samples can be analyzed by Raman spectroscopy.
 Liquid samples can be held in beakers, test tubes, glass capillary tubes, or
NMR tubes.
 Aqueous solutions can be analyzed, since water is a very weak Raman
scatterer. This is an advantage for Raman spectroscopy over IR.
 Other solvents that can be used for Raman studies include chloroform,
carbon tetrachloride, acetonitrile, and carbon disulfide.

9. 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.
 Now Raman spectrometers being marketed are either Fourier transform
instruments equipped with cooled germanium transducers or multichannel
instruments based upon charge-coupled devices.

10. APPLICATION
 Quantitative and qualitative analyses of inorganic and organic compounds
can be performed by Raman spectroscopy.
 Raman spectroscopy is used for bulk material characterization, online
process analysis, microscopic analysis, and chemical imaging of inorganic,
organic and organometallic compounds, polymers, biological systems etc.
 Raman spectra have fewer lines and much sharper lines than the
corresponding IR spectra. This makes quantitative analysis, especially of
mixtures, much simpler by Raman spectroscopy than by IR spectroscopy.
 Another use of Raman spectroscopy for quantitative analysis is the
determination of percent crystallinity in polymers.

11.  Quantitative analysis requires measurement of the intensity of the Raman
peaks and the use of a calibration curve to establish the concentration –
intensity relationship. The intensity of a Raman peak is directly proportional
to the concentration.

12. REFERENCE
1. Robinson W. J. & Frame S. M. E.: Undergraduate Instrumental Analysis,
Sixth Edition: 290-302

13. OPEN TO DISCUSSION

14. THANK YOU