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1. J.C.BOSE UNIVERSITY OF SCIENCE AND TECHNOLOGY, YMCA, FARIDABAD PRESENTATION ON STUDY OF RAMAN SPECTROSCOPY SUBMITTED TO : SUBMITTED BY : MONIKA ROLL NO - 21001752031

2. CONTENTS Introduction Principle Mechanism of Raman scattering Instrumentation Analysis of Raman Spectrum of Polyaniline Difference between Raman and Infrared spectroscopy Advantages and disadvantages Applications 6/8/2023 Sample Footer Text 2

3. INTRODUCTION Raman Spectroscopy is a spectroscopic technique based on the Raman Scattering Effect. It was discovered by the Indian Physicist Sir C.V. Raman in 1928. When radiation passes through a transparent medium , the species present scatter a fraction of the beam in all directions. Raman discovered that the visible wavelength of the small fraction of the radiation scattered by certain molecules differs from that of the incident beam and furthermore that the shifts in wavelength depend upon the chemical structure of the molecules responsible for the scattering. Raman spectroscopy is an important tool in scientific research due to its ability to provide detailed information about the molecular structure and composition of materials. Raman Spectroscopy is a versatile technique that can be used to analyse a wide range of materials, including solids, liquids, and gases, and it can provide both qualitative and quantitative information about a sample. 6/8/2023 3

4. PRINCIPLE OF RAMAN SPECTROSCOPY Raman scattering, also known as Raman spectroscopy, is a spectroscopic technique used to study the vibrational, rotational, and other low-frequency modes in a system. When light interacts with a material, some of it is scattered in different directions. In Raman scattering, the scattered light undergoes a shift in frequency that is characteristic of the vibrational energy levels in the material. The Raman effect is based on the inelastic scattering of photons by a material. When a photon interacts with a molecule, it can excite the molecule to a higher energy level. In the Raman effect, the scattered photon has a different energy than the incident photon due to this excitation. The energy difference between the incident and scattered photons corresponds to the energy of a particular vibrational mode in the molecule.

5. In Raman spectroscopy, there are two types of Raman scattering: Stokes and anti-Stokes. Both types involve the interaction of a photon with a material, but they differ in the energy of the scattered photon. STOKES RAMAN SCATTERING Stokes Raman scattering occurs when a photon is scattered with a lower energy (longer wavelength) than the incident photon. This is the most common type of Raman scattering. It occurs when a molecule is excited from its ground state to a higher energy state by the incident photon. The scattered photon is then emitted as the molecule returns to its original ground state. The energy lost by the molecule during the scattering process is equal to the energy of a vibrational mode, and this is reflected in the frequency shift of the scattered photon.

6. ANTI-STOKES RAMAN SCATTERING Anti-Stokes Raman scattering, on the other hand, occurs when a photon is scattered with a higher energy (shorter wavelength) than the incident photon. This type of scattering is less common and occurs when the molecule is already in an excited state before the incident photon arrives. The scattered photon is then emitted as the molecule loses energy during its return to the ground state. The energy gained by the molecule during the scattering process is also equal to the energy of a vibrational mode, and this is reflected in the frequency shift of the scattered photon. RAYLEIGH SCATTERING Rayleigh scattering refers to the scattering of light by particles in its path of size up to one-tenth the wavelength of the light and occurs without any loss of energy or change of wavelength.

7. EXCITATION OF RAMAN SPECTRA The abscissa of Raman spectrum is the wavenumber shift Av, which is defined as the difference in wavenumbers (cm-1) between the observed radiation and that of the source. For CCI, three peaks are found on both sides of the Rayleigh peak and that the pattern of shifts on each side is identical . Anti-Stokes lines are appreciably less intense that the corresponding Stokes lines. For this reason, only the Stokes part of a spectrum is generally used. The magnitude of Raman shifts are independent of the wavelength of excitation.

8. MECHANISM OF RAMAN AND RAYLEIGH SCATTERING The heavy arrow on the far left depicts the energy change in the molecule when it interacts with a photon. The increase in energy is equal to the energy of the photon hv. The second and narrower arrow shows the type of change that would occur if the molecule is in the first vibrational level of the electronic ground state. The middle set of arrows depicts the changes that produce Rayleigh scattering. The energy changes that produce stokes and anti-Stokes emission are depicted on the right. The two differ from the Rayleigh radiation by frequencies corresponding to +^E, the energy of the first vibrational level of the ground state. If the bond were infrared active, the energy of its absorption would also be AE. Thus, the Raman frequency shift and the infrared absorption peak frequency are identical.

9. INSTRUMENTATION Instrumentation for modern Raman spectroscopy consists of three components: A laser source a sample illumination system a suitable spectrometer. 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.

10. FIG : SCHEMATIC OF RAMAN SPECTROMETER

11. Sample Illumination System Sample handling for Raman spectroscopic measurements is simpler than for infrared spectroscopy because glass can be used for windows, lenses, and other optical components instead of the more fragile and atmospherically less stable crystalline halides. In addition, the laser source is easily focused on a small sample area and the emitted radiation efficiently focused on a slit. Consequently, very small samples can be investigated. A common sample holder for non absorbing liquid samples is an ordinary glass melting-point capillary. 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.

12. Analysis of Raman spectrum of polyaniline The Raman Spectroscopy has also been utilized for the analysis of molecular structure of the analysis of molecular structure of the deposited PAni thin films. Fig. shows the Raman spectra of an organic material (polyaniline). The peak observed at 1593 cm-1 is assigned to stretching mode of quinoid rings. The band is observed at 1502cm-1 is related to the C=N vibrations of quinoid ring with the emeraldine base form of PAni. The peak observed at 1401cm-1 can be attributed to the reduced state of PAni.

13. RAMAN VS INFRARED RAMAN It is due to the scattering of light by the vibrating molecules. The vibration is Raman active if it causes a change in polarisability. The molecule need not possess a permanent dipole moment. Water can be used as a solvent. Sample preparation is not very elaborate, it can be in any state. Gives an indication of covalent character in the molecule Cost of instrumentation is very high INFRARED It is due to the scattering of light by the vibrating molecules. The vibration is Raman active if it causes a change in polarisability The molecule need not possess a permanent dipole moment. Water can be used as a solvent. Sample preparation is not very elaborate, it can be in any state. Gives an indication of covalent character in the molecule. Cost of instrumentation is very high

14. ADVANTAGES AND DISADVANTAGES OF RAMAN SPECTROSCOPY ADVANTAGES Non-destructive : Raman spectroscopy is a non-destructive technique, which means that it does not require any sample preparation or chemical modification of the sample. Structural information: Raman spectroscopy provides structural information about the sample, such as bond lengths, bond angles, and torsional angles. Minimal sample preparation: Raman spectroscopy requires minimal sample preparation, which makes it a convenient and cost-effective technique. Versatility: Raman spectroscopy can be used to analyse a wide range of samples, including liquids, solids, gases, and biological tissues. DISADVANTAGES Low signal intensity: Raman scattering is an inherently weak process, and the Raman signal can be very weak compared to the background noise. Instrumentation cost: High-quality Raman spectrometers can be expensive, which can limit access to the technique for some researchers. Fluorescence interference: One of the main limitations of Raman spectroscopy is fluorescence interference. Many samples exhibit fluorescence, which can interfere with the Raman signal and obscure the spectral features. Spatial resolution: The spatial resolution of Raman spectroscopy is limited by the diffraction limit of the optical system, which can make it difficult to analyze small features or structures.

15. Applications of Raman spectroscopy Material science: Raman spectroscopy is widely used in the study of materials science, including the analysis of polymers, ceramics, semiconductors, and carbon-based materials such as graphene and carbon nanotubes. Pharmaceutical industry: Raman spectroscopy is used extensively in the pharmaceutical industry for drug development, quality control, and counterfeit detection. Raman spectroscopy can be used to identify the active ingredients in drugs, analyze drug formulations, and detect impurities and contaminants. Biomedical research: Raman spectroscopy has numerous applications in biomedical research, including the analysis of tissues, cells, and biomolecules such as proteins and nucleic acids. Raman spectroscopy can provide information on the chemical composition and structure of these biological samples, and can be used for disease diagnosis and monitoring. Forensic science : Raman spectroscopy is used in forensic science for the analysis of trace evidence such as fibers, paint chips, and drugs. Raman spectroscopy can provide information on the chemical composition and structure of these materials, which can be used to link them to a crime scene or suspect. Environmental science: Raman spectroscopy is used in environmental science for the analysis of pollutants and contaminants in air, water, and soil. Raman spectroscopy can be used to identify and quantify these contaminants, and to monitor environmental changes over time.

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