This document provides an overview of Raman spectroscopy. It begins with a brief history noting its discovery in 1928 by Raman for which he later won a Nobel Prize. It then covers the basic principles of Raman spectroscopy including the Raman effect, Stokes and anti-Stokes scattering. Instrumentation components like lasers, filters, and detectors are described. Different types of samples that can be analyzed including solids, liquids, and gases are mentioned. Finally, applications of Raman spectroscopy in various fields like chemistry, polymers, mixtures, inorganic/organic species, and biology are highlighted.

1. RAMAN SPECTROSCOPY
Presented by
• Kamal Lochan Misra
• Roll No. 2208257020
• M. Pharm 2nd Semester
• Department of Pharmaceutical Chemistry
• Institute of Pharmacy and Technology, Salipur,
Cuttack

2. CONTENT
 Introduction
 Principle
 Instrumentation
 Types of sample in Raman
 Difference between IR and Raman
 Difference types of Raman
 FTSR
 Applications

3. • The Raman effect underlying Raman spectroscopy is
ancient and was discovered in 1928 by Dr. Raman in
India, who later won the Nobel Prize. However,
because the intensity of the scattered light is very
weak relative to the incident light (excitation light),
there was no practical light source for Raman
spectroscopy until the invention of the laser of the
1960s.
• In the late 1970’s, microscopic Raman with an
optical microscope equipped with a Raman
spectrometer appeared, and it was used in many
fields as a local analysis tool.

4. INTRODUCTION
 Raman spectroscopy was discovered by C.V. Raman in 1928.
 It is a spectroscopic technique used to observe the rotational, vibrational, and other low
frequency modes in a system.
 It is commonly used in chemistry to provide a fingerprint by which molecules can be identified.
 When the beam passed through the transparent region the species present scatter a region of the
beam in all directions.
 Raman scattering result from the same type of quantities vibration changed associated with IR
spectra.

6. PRINCIPLE
• The monochromatic radiation is passed through the sample such that the radiation may get reflected,
absorbed, or scattered in some manner. It is the scattering of radiations which gives information about
molecular structures.
• The scattered photons have a different frequency from the incident photon as the vibration and
rotational property vary.
• The spectrum is measured with the laser line as reference. Hence, the peak are measured as
shift from the laser line.
• The peak positions are determined by the vibrotational energies associated with the bonds in
the molecules of which sample is composed. Because of this, the spectrum end up looking
very similar to IR spectra and is interpreted similarly.
• The bonds that are emphasized in Raman spectrum are those that are due to highly polarizable
bonds such are those π electrons.

7. • The emitted radiations are of 3 types: 1. Stokes scattering.
2. Anti-Stokes scattering.
3. Rayleigh scattering
• Raman is based on scattering. The sample is irradiated with a coherent source typically a laser.
Most of radiations is elastically scattered (called the Rayleigh scatter).
• A small portion is elastically scattered (Raman scatter, composed of stokes and anti-stokes
portion).
• The difference between the incident photon and the scattered photon is known as the Raman
shift.
• When the energy associated with the scattered photons is less than the energy of an incident
photon, the scattering is known as Stokes scattering.
• When the energy of the scattered photons is more than the incident photon, the scattering is
known as Anti-stokes scattering.

14. INSTRUMENTATION

16. Raman spectroscopy consist of this major components :
1. Excitation source (laser)
Raman spectroscopy uses a laser as a light source. The radiation of the spectrum depends upon the bandwidth of the
laser source used. Generally, a shorter wavelength gives stronger Raman scattering.
2. Sample
A sample is placed in the sample chamber that accepts the laser and it undergoes scattering, both elastic and inelastic
which further passes through the filter.
3. Filter
A filter is used in Raman spectroscopy to separate the Raman scattered light from the Rayleigh scattered light. This is
done to get high-quality Raman spectra. Some filters are notch, long pass, and volume halogen filters.
4. Detector
Detector helps to detect the scattered light signal. Generally, LCD array detectors are used in modern Raman
spectrometers. They are optimized to detect signals of different wavelengths and even detect very weak signals.
5. Computer
A computer having suitable compatible software helps to draw a final Raman spectroscopy graph/ spectrum.

18. Types of Samples In Raman :
Solid : Solid samples are acquired by filling a small cavity with the sample after is has
been ground to a fine powder. Polymer can usually be examined directly with no sample
pretreatment.
Liquid : The major advantage of sample handling in Raman spectroscopy compared to
Infrared arises because water is a weak Raman scattered but a strong absorber of infrared
radiations. Thus, aqueous solutions can be studied in Raman spectroscopy but not in
infrared.
• This advantage is particularly important for biological and inorganic systems and in
studies dealing with water pollution problems.
Gas : Gas are normally contained in a glass tubes, 1-2cm in diameter and about 1mm in
thick. Gas can also be sealed in small capillary tubes.

20. RAMAN SPECTRUM

21. DIFFERENT TYPES OF RAMAN SPECTROSCOOPY
1. Resonance Raman Spectroscopy (RRS)
2. Surface-enhanced Raman Spectroscopy (SERS)
3. Micro Raman Spectroscopy
4. Non-linear Raman Spectroscopic technique

22. Fourier Transform Raman Spectroscopy
• Raman instrument can be on the same bench as FTIR.
• Often, a YAG:Nd3+ laser (1064nm) is used to excite the sample, so that the excitation energy is
lower than the absorption band energies of organic systems.
• Fluorescence is then minimized.
• Instruments can be combined with a microscope, or optical
fibre so that scanning over a few (microns) 2 of surface
area and Raman mapping is easily performed.

24. APPLICATION OF RAMAN SPECTROSCOPY
1. It is used to study the structure of CO₂, N₂O, mercurous salts, chloro complexes of mercury,
and the nature of bonding.
2. It help to study physical chemistry concerning electrolytic dissociation, hydrolysis, and
transition from crystalline to amorphous state.
3. It is also used to obtain information regarding the presence or absence of specific linkages in a
molecule, the structure of simple compounds, and the study of isomers.
4. It is used for the characterization of polymer compounds by revealing the physical properties
like polymer crystallinity, tacticity, amorphous character, etc.
5. It can be easily used for rapid, easy, and accurate analysis of mixtures that are difficult with
any other method.

25. RAMAN SPECTRA FOR INORGANIC SPECIES
• This technique is often superior to infrared for investigating inorganic system because aqueous
solutions can be employed.
• In addition, the vibrational energies of metal-ligand bonds are generally in the range of 100 to
700 cm-1, a region of the infrared that is experimentally difficulty too study.
• These vibrations are frequently Raman active however and the peaks with ∆v values in this
range readily observed.
• Raman studies are potentially useful sources of information concerning the composition,
structure and stability of coordination compounds.

26. RAMAN SPECTRA FOR ORGANIC SPECIES
• Raman spectra are similar to infrared spectra in that they have regions that are useful for
functional group detection and fingerprint region.
• Raman spectra yield more information about certain types of organic compounds than do their
infrared counter-parts.
QUANITATIVE APPLICATIONS
• Raman sampling devices are not subjected to attack by moisture and small amount of water in a
sample don't interfere.

27. BIOLOGICALAPPLICATION OF RAMAN SPECTROCOPY
• Raman spectroscopy has been widely used for study of biological system.
• The advantage of this technique include the small requirement, minimal sensitivity
toward interference by water, the spectral detail, and the confirmational and
environment sensitivity.

29. Thank you