Intro Raman Scattering

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This presentation was used to introduce Resonance Raman Scattering to physical chemistry graduate students

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Intro Raman Scattering

  1. 1. Scattering of Light: Raman Spectroscopy Deanna O’Donnell Informal P-Chem Review June 9 th , 2009
  2. 2. A review of light <ul><li>Electromagnetic wave </li></ul><ul><ul><li>Oscillating electric and magnetic fields </li></ul></ul><ul><li>Classical Interactions of light and matter </li></ul><ul><ul><li>Absorption </li></ul></ul><ul><ul><li>Reflection </li></ul></ul><ul><ul><li>Refraction </li></ul></ul><ul><ul><li>Scattering </li></ul></ul><ul><li>Scattering </li></ul><ul><ul><li>Elastic (Rayleigh scattering) </li></ul></ul><ul><ul><li>Inelastic (Raman scattering) </li></ul></ul>
  3. 3. History <ul><li>Sir. C.V. Raman discovered light scattering in 1928 </li></ul><ul><li>Awarded Nobel Prize in physics in 1930 </li></ul><ul><li>Experiment composed of light source ( sunlight ), a sample, and detector ( eye ) </li></ul><ul><li>His nephew, Dr. S. Chandrasekhar, of the University of Chicago won the Nobel prize in physics in 1983 </li></ul>Sir. C.V. Raman
  4. 4. Raman Basics <ul><li>Raman spectroscopy studies the frequency change of light due to the interaction with matter </li></ul><ul><li>The energy of a vibrational mode (  m ) depends on molecular structure and environment. </li></ul><ul><ul><li>Atomic mass, Bond order, Molecular substituents, Molecular geometry and Hydrogen bonding all contribute </li></ul></ul><ul><li>Raman signal is 10 -6 time weaker than incident light (  o ) </li></ul><ul><li>Photons are not absorbed </li></ul><ul><li>To observe Raman scattering the molecule must be polarizable </li></ul>
  5. 5. Raman Basics <ul><li>Raman shifts can be expressed as  o ±  m </li></ul><ul><ul><li>Stokes and Anti-stokes produce same spectrum, differing in intensity. Intensity is governed by the Maxwell-Boltzmann Distribution law. </li></ul></ul><ul><li>Raman shifts are measured in wavenumbers ( cm -1 ) </li></ul>Stokes and Anti-stokes Raman Spectrum of CCl 4 E 1 E 0 Stokes Scattering Anti-Stokes Scattering Rayleigh Scattering   -  m   +  m   virtual states
  6. 6. More Raman Basics <ul><li>S 1 </li></ul><ul><li>S o </li></ul><ul><li>S o </li></ul>Normal Raman  ≤ 10 0 Resonance Raman  ≥ 10 3 Energy  o = 500nm  o = 334nm
  7. 7. Signal Enhancement <ul><li>Common method to enhance the Raman scattering is </li></ul><ul><ul><li>Resonance Raman </li></ul></ul><ul><li>Resonance Raman </li></ul><ul><li>Occurs when  o   em </li></ul><ul><li>Enhancement is on the order of 10 3 to 10 8 </li></ul> i =  ij E j  i = induced electric dipole  ij = polarizability E = electric field of the iiiiiiiiii electromagnetic radiation I mn = I o (  o -  mn ) 4  |(  ij ) mn | 2 (  ij ) mn  (  em -  o ) -1 http://www.personal.dundee.ac.uk/~tjdines/Raman/RR3.HTM
  8. 8. Resonance Raman Intensity I mn = I o (  o -  mn ) 4  |(  ij ) mn | 2 (  ij ) mn  (  em -  o ) -1
  9. 9. Example of Frank-Condon Factors <ul><li>The Journal of Chemical Physics, Vol. 118, No. 3, pp. 1378–1391, 2002 </li></ul>Electronic structure of para aminophenoxyl radical in water - G. N. R. Tripathi A = Absorption Spectrum of p-aminophenoxyl radical
  10. 10. TR-RR Data Collection  scattered 440 nm ± 30 nm  incident 440 nm Background: H 2 O, sodium benzoate, t-butanol,KOH (pH = 13.2), degassed with N 2 Signal + Background: H 2 O, sodium benzoate, t-butanol, KOH (pH = 13.2), degassed with N 2 , and benzoate dianion
  11. 11. TR-RR Data Analysis
  12. 12. Good References <ul><li>Vibrational Spectroscopy </li></ul><ul><ul><li>Wilson, E.B.; Decius, J.C.; Cross, P.C.; Molecular Vibrations , </li></ul></ul><ul><ul><li>ISBN:0-486-63941-X </li></ul></ul><ul><ul><li>Harris, D.C.; Bertolucci, M.D.; Symmetry and Spectroscopy , </li></ul></ul><ul><ul><li>ISBN: 0-486-66144-X </li></ul></ul><ul><li>Raman Spectroscopy </li></ul><ul><ul><li>Ferraro, J.R.; Nakamoto, K.; Brown, C.W.; Introductory Raman Spectroscopy , ISBN: 978-0-12-254105-6 </li></ul></ul><ul><ul><li>Aroca, Ricardo, Surface Enhanced Vibrational Spectroscopy , </li></ul></ul><ul><ul><li>ISBN: 978-0-47-160731-1 </li></ul></ul><ul><li>Radiation Chemistry Rates </li></ul><ul><li>Buxton, et al. J. Phys. Chem. Ref. Data , Vol. 17, No. 2, 1988 </li></ul><ul><li>(QC1.J6 in Notre Dame Radiation Library) </li></ul><ul><li>Notre Dame Radiation Laboratory – Radiation Chemistry Data Center </li></ul><ul><li> www.rcdc.nd.edu/ (use index, search engine not reliable) </li></ul>

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