raman spectroscopy 2.pptx

Raman spectroscopy
Thamina khan
M . Pharm. 1st yr
2nd sem
pharmaceutical chemistry

1. Department of Pharmaceutical Sciences Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur - 440033 Topic: RAMAN SPECTROSCOPY PRESENTED BY TAHMINA KHAN M. PHARM. FRIST YEAR PHARMACEUTICAL CHEMISTRY

2. content INTRODUCTION PRINCIPLE QUANTUM THEORY OF RAMAN SCATTERING INSTRUMENTATION RAMAN SPECTRUM COMPARISON BETWEEN RAMAN AND IR SPECTROSCOPY APPLICATION REFERENCE 2 RAYLEIGH SCATTERING STOKES SCATTERING ANTI-STOKES SCATTERING

3. INTRODUCTION Raman spectroscopy was discovered by C. V. Raman in 1928. He was awarded by Noble prize in 1930 and Bharat ratan in 1954 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

4. PRINCIPLE When monochromatic radiation is incident upon a sample then this light will interact with the sample in some fashion. It may be reflected, absorbed or scattered in some manner. It is the scattering of the radiation that occurs which gives information about molecular structure. Raman is based on scattering . The sample is irradiated with a coherent source, typically a laser. Most of the radiation is elastically scattered (called the Rayleigh scatter).
A small portion is inelastically scattered (Raman scatter, composed of Stokes and anti-Stokes portions). This latter portion is what we are particularly interested in because it contains the information in which are interested. 5

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6. Quantum Theory Of Raman Scattering The emitted radiation is of three types Rayleigh scattering 7 There is no net absorption or Emission of light the Output =input hv s = hv I v s = v i

7. 2. Stokes scattering 8 There is net absorption of rad. So Scattered Energy = Input-absorbed Energy hv s = hv I -hv o v s < v i

8. 3. Anti-stokes Scattering 9 There is net absorption of rad. So Scattered Energy = Input- Emitted Energy hv s = hv I + hv o v s > v i

9. Raman spectrometer 10

10. INSTRUMENTATION 11

11. INSTRUMENTATION Instrumentation for modern Raman spectroscopy consists of following components: Laser or source of light Filter
Sample Optics Monochromator Suitable spectrometer (Detector) 12

12. 13 Laser or source of light Laser are generally the only source strong enough to scatter lots of light and lead to detectable in Raman spectroscopy. 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.

13. S.No . Laser wavelength 01 Nd:YAG 1064nm 02 Helium : Neon 633nm 03 Argon ion 488.0 or 514.5nm 04 Ga:Al:As diode 785.0 or 830.0nm 05 Krypton 530.9 or 647.1mn 14 List of Various Laser Source

14. 2) FILTER It is used to eliminated unwanted radiations. For getting monochromatic radiation filters used. They may be made of Nikel oxide, glass or quartz glass. Sometimes a suitable coloured solution such as an aqueous solution of ferri cyanide or iodide in CCl2 may be used as monochromator. 15

15. 3) Sample Optics : For study Raman effects the type of sample holder to be used depends upon intensity of light , nature and availability of solvent . 1. For Liquid Samples : A major advantage of sample handling in Raman spectroscopy compared with infrared arises because water is a weak Raman scattered 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. 16

16. 2. For Solid Samples : Solid sample used in Raman spectroscopy is in the form of pellets and powders. 3. For Gas samples : Gases required sample optics bigger than those for liquid. (for more quantity) Gas are normally contain in glass tubes, 1-2 cm in diameter and about 1mm thick. Gases can also be sealed in small capillary tubes 17

17. monochromator Raman spectroscopy incorporate two or more grating monochromators It is used: To increase the resolving power of spectrometer. To reduce background caused by Rayleigh scattering by the sample. 18

18. 4) Raman Spectrometers Raman spectrometers were similar in design and used the same type of components as the classical ultraviolet/visible dispersing instruments i.e photomultiplier or photocounting Most employed double grating systems to minimize the spurious radiation reaching the transducer. Photomultipliers served as transducers.
In this photon incident on photocathode causes the emission of electron, the number emitted being proportional to that of photon ,and the amplify the signal in recorder. 19

19. Photomultiplier 20

20. Raman spectrum Typical Raman spectrum (of CCl 4 ) • Plot of signal intensity (y-axis) vs Raman shift(x-axis) ( 21

21. Peak position The 4000-2500 cm -1 is the region where single bonds (X-H) absorb The 2500-2000 cm -1 ,is referred to as the multiple bond (-N=C=O ) region The 2000-1500 cm -1 , region is where double bond (-C=O, -C=N , -C=C- ) occur Below 1500 cm -1 , some group e.g. nitro (O=N=O) do have specific bonds but many molecule have complete pattern of Carbon –Carbon and Carbon-Nitrogen vibrations . The region is generally referred to as the fingerprint region . The significant bond below 650 cm -1 usually arise from inorganic group , metal organic group or lattice vibration. 22

22. Comparison between raman and ir spectroscopy RAMAN SPECTROSCOPY IR SPECTROSCOPY Analysis of scattered light of the vibrating molecule Analysis of absorption of the vibrating molecule. Vibration is Raman active if it causes a change in the polarizability Vibration is IR active if change in the dipole moment during the vibration occurs Molecules may not have a dipole moment chemical bond must have the characteristic of an electric dipole . Water can be used as solvent. Water can not be used as solvent due to intense absorption. No need for specific sample preparation. Required specific sample preparation. Expensive instrumentation costs are relatively very high. Relatively expensive instrumentation. 23

23. APPLICATION 1. Raman Spectra of Inorganic Species The Raman technique is often superior to infrared for spectroscopy investigating inorganic systems 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 difficult to study. 4. Biological Applications of Raman Spectroscopy Raman spectroscopy has been applied widely for the of biological systems. The advantages of his technique include the small sample requirement, the minimal sensitivity toward interference by water, the spectral detail, and the conformational and environmental sensitivity. 24

24. 2. Raman Spectra of Organic Species Raman spectra are similar to infrared spectra in that they have regions that are useful for functional group detection and fingerprint regions that permit the identification of specific compounds. Raman spectra yield more information about certain types of organic compounds than do their infrared counterparts. 3. Quantitative applications Raman spectra tend to be less cluttered with peaks than infrared spectra. As a consequence, peak overlap in mixtures is less likely, and quantitative measurements are simpler. In addition, Raman sampling devices are not subject to attack by moisture, and small amounts of water in a sample do not interfere. 25

25. WHY RAMAN SPECTRA IS BETTER THAN OTHER? Rotational spectroscopy is observed for the substance is Gaseous state, Vibrational spectra can be observed for gaseous & Liquid state however Raman Spectra can be used with solids, liquids or gases. Raman Spectra can be used obtained even for O 2 , N 2 , C 12 etc. which have no permanent dipole moment. Such a study has not been possible by IR spectroscopy. Raman spectra is independent of incident frequency. It can be obtained for visible spectrum range which is easy to adjust rather than IR or radio waves. No sample preparation needed. Not interfered by water. Non-destructive. Highly specific like a chemical fingerprint of a material. Raman spectra are acquired quickly within seconds. Samples packaging. Can be analyzed through glass or a polymer. 26

26. REFERENCE Instrumental Analysis by Skoog Holler Crouch; 533-550
Elementary Organic Spectroscopy Y R Sharma ; 164-190 Purohit, Vishwas. “ Sir C.V.Raman and Raman Spectroscopy (1888-1970). ” Buzzle.com. 1 Apr. 2005. 19 Apr. 2009 http://www.buzzle.com/editorials/4-1 2005-67909.asp . 27

27. Thank you. 28