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30120140504010 2 30120140504010 2 Document Transcript

  • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 83-89 © IAEME 83 A REVIEW ON RAMAN EFFECT ITS APPLICATIONS AND SPECTRUM & TO STUDY INFRARED AND RAMAN SPECTROSCOPY Dr GURUDUTT SAHNIa , BALPREET SINGHb a (HOD & DGM (Design, Drawing & Development) LEADER VALVES LTD JALANDHAR, PUNJAB, INDIA) & C Eng (INSTITUTION OF ENGINEERS INDIA) b (SCHOLAR, DEPTT OF MECH ENGG (100101128373) BEANT COLLEGE OF ENGG & TECH GURDASPUR, PUNJAB, INDIA) ABSTRACT The Raman effect is the appearance of weak lines in the spectrum of light scattered by a substance which has been illuminated by a monochromatic light (with angular frequency ω).The lines occur close to, and on each side of, the incident light frequency, and hence are optical sidebands. The sidebands arise from the nonlinear interaction of the light with atomic or molecular quantum states in the scattering material. Because this theory was invented by sir C.V. Raman and he got the noble prize for that in physics. The phenomenon is named for Indian physicist Sir ChandrasekharaVenkata Raman, who first published observations of the effect in 1928. (Austrian physicist Adolf Smekal theoretically described the effect in 1923. MAIN OBJECTIVES ARE 1. TO STUDY RAMAN EFFECT 2. TO STUDY INFRARED AND RAMAN SPECTROSCOPY 3. TO STUDY APPLICATIONS OF RAMAN SPECTROSCOPY 4. TO STUDY RAMAN SPECTRUM AND ADVANTAGES Keywords: RAMAN, SPECTROSCOPY. INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 5, Issue 4, April (2014), pp. 83-89 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2014): 7.5377 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 83-89 © IAEME 84 INTRODUCTION Light as a probe of molecular structure 1. light is absorbed → excitation of molecule 2. de-excitation of molecule → light is emitted • visible/UV: excitation of valence electrons • infrared (IR):excitation of vibrations • microwave/IR:excitation of rotations APPLICATIONS Raman Spectroscopy is a method of determining modes of molecular motions, especially motions, especially vibrations. It is predominantly applicable to the qualitative and quantitative analyses of covalently bonded molecules. Various applications are as follows MICROWAVE INRAREDVISIBLE & ULTRAVIOLET
  • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 83-89 © IAEME 85 HEADING TOWARDS SPECTROSCOPY THERE ARE TWO TYPES OF SPECTROSCOPY AS FOLLOWS Characteristic regions for different groups as in IR GOOD FOR AQUEOUS BASED SAMPLES Raman databases available IDENTIFICATIO N OF PHASES Useful for a variety of samples, organic, inorganic & biological MOLECULAR AND CRYSTALINE SYMMETRIES MEASUREMEN T OF STRESS Identification of crystalline polymorphs TYPES OF SPECTROSCOPY INFRARED SPECTROSCOPY RAMAN SPECTROSCOPY
  • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 83-89 © IAEME 86 1. Aspectrum is a graph of light intensity as a function of light frequency 2. From molecular structure, the compound can be identified STARTING WITH IR SPECTROGRAPHY RAMAN SPECTROGRAPHY TO BE NOTED 1. Spectra shows vibrational frequency in wavenumbers (cm-1) 2. Peaks are used to identify chemical "groups", i.e. types of bonds 3. Examples of characteristics group stretching frequencies Peaks in the spectrum give information about molecular structure IR SPECTROGRAPHY ABSORPTION RAMAN SPECTROGRAPHY SCATTERING
  • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 83-89 © IAEME 87 O-H 3600 cm-1 N-H 3400 cm-1 C-H 3000 cm-1 C-O/C-N/C-C 1100-1200 cm-1 C-C 1200 cm-1 aromatic C-C 1450-1600 cm-1 C=C 1650 cm-1 C≡C 2200 cm-1 1. Raman based on inelastic scattering of a monochromatic excitation source as • Routine energy range: 200 - 4000 cm–1 • The Raman effect comprises a very small fraction, about 1 in 10^7 of the incident photons Great for many real-world samples - Minimal sample preparation (gas, liquid, solid) - Compatible with wet samples and normal ambient - Sample fluorescence is problematic Raman Spectrum A Raman spectrum is a plot of the intensity of Raman scattered radiation as a function of its frequency difference from the incident radiation (usually in units of wavenumbers, cm-1). This difference is called the Raman shift. At the very most, the intensities of Raman lines are 0.001 % of the intensity of the source; as a consequence, their detection and measurement are somewhat more difficult than are infrared spectra SELECTION RULES FOR IR SPECTROSCOPY SELECTION RULES DICTATE WHICH MOLECULAR VIBRATIONS ARE PROVIDED SOME VIBRATIONS ARE MADE OF BOTH IR AND RAMAN EFFECT
  • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 83-89 © IAEME 88 1. The intensity or power of a normal Raman peak depends in a complex way upon the polarizability of the molecule, the intensity of the source, and the concentration of the active group. 2. The power of Raman emission increases with the fourth power of the frequency of the source. 3. Raman intensities are usually directly proportional to the concentration of the active species. STOKES AND ANTISTOKES I N T E N S I T Y Raman Spectrum of CCl4 RAYLEIGH I N T E N S I T Y Raman Spectrum of CCl4(488.0 NM EXCITATION) RAMAN SHIFT
  • International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online), Volume 5, Issue 4, April (2014), pp. 83-89 © IAEME 89 Advantages of Raman 1. Selection rules allow for some vibrations (normally symmetric) to be seen only by Raman spectroscopy. 2. Measurements of depolarization ratios yield information about molecular symmetry. 3. Water is a weak Raman scatterer, allowing for the use of aqueous solutions. Can also sample through glass container walls. CONCLUSION 1. The region 4000 cm-1 to 50 cm-1 can be covered in a single scan without changing gratings, splitters,detectors, etc. 2. Only a small sample area is needed (laser spot) 3. Application of Raman Effect - Geology, Material Science, Petrochemistry, polymers, Pharmaceutical Industry, NuclearScience, Forensic Science. REFERENCES 1. Raman: theory and Raman: theory and instrumentation Kit Umbach Dept. of MS&E Dept. of MS&E CCMR, NBTC facilities. 2. C.V. Raman and K.S. Krishnan, Indian J. Phys. 2, 387 (1928) 3. P.Straughan and S. Walker, Spectroscopy(Chapman and Hill, London, 1962), Vol.2, 198, pg 225-258 4. S. Walker and H. Straw, Spectroscopy(Chapman and Hill, London, 1962) Vol. 2, p. 176. 5. A. Anderson, ed., The Raman Effect(Marcel Dekker, New York, 1971). As you can see, the Stokes peaks correspond to lower photon frequencies and lower energies. The anti-Stokes side is symmetric but corresponds to higher frequencies and energies. The Stokes lines are stronger because the population of molecules at ν=0 is much larger than at ν =1 by the Maxwell- Boltzmann distribution law.