Raman Spectroscopy

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Raman Spectroscopy

  1. 1. Matt Bloodgood David Watts
  2. 2. Outline Background – C.V. Raman and discovery  What Raman scattering is and how it works  How it is used for spec.  What does it show  Our experiments  Data  Future Directions – how data to be used  Summary  References 
  3. 3. Chandrashekhar Venkata Raman Born Nov. 7th, 1888 in Southern India   1907 – was posted in Calcutta as Assistant Accountant General; 30 papers.  Research – acoustics and optics  Pioneered Indian science – founded Indian Academy of Sciences, found Indian Journal of Physics (editor) Figure 1. C.V. Raman (Purohit)
  4. 4. Discovery 1921 – return trip over Mediterranean Sea   Why blue; Rayleigh – reflection from sky 1922 – published results; Raman scattering  born.  March of 1928, Raman refined experiment  discovered Stokes shifts (Mercury arc lamp).
  5. 5. What is Raman Scattering? Scattering of incident light – inelastic   Rayleigh vs. Raman scattering Figure 2. Jablonski Diagram of Rayleigh and Raman Scattering. (Chumanov 5)
  6. 6. Stokes and Anti-Stokes Shifts Stokes shifts – red shift due to absorbed  energy  Anti-Stokes – blue shift due to energy given  Nuclei vibrations – ω  Resonant Raman scattering Figure 3. Polarization by an Electromagnetic Wave. (Chumanov 2)
  7. 7. What Can Raman Do For Us? Molecular analysis – each molecule has  a distinct spectrum  Atomic bonds  distinct  Vibrational frequency of nuclei Qualitative Results   What is there, what is happening? Can show progress of a reaction 
  8. 8. Spectrometer details
  9. 9. Raman Data Data presented relative to excitation  frequency.  Wavelength  frequency (cm-1)  Example:
  10. 10. Raman Spectroscopy Experiments Acid-Base   Objective: To analyze vibrational shift caused by hydrogen extraction using Raman spectroscopy Water-Ethanol Systems   Objective: To analyze the effect on Raman scattering of different water-ethanol solutions Highly Qualitative 
  11. 11. Acid-Base Experimental Glacial Acetic Acid  OH- was used to deprotonate Acetic  Acid Acetate Ion
  12. 12. Acetic Acid Spectrogram Acetic Acid (CH3COOH) 500 450 400 Counts 350 300 250 500 700 900 1100 1300 1500 1700 Wavelength (nm)
  13. 13. Acetate Spectrogram Conjugate Base (CH3COO-) 500 450 400 Counts 350 300 250 500 700 900 1100 1300 1500 1700 Wavelength (nm)
  14. 14. Acid Base Overlay Acetic Acid – Acetate Overlay 500 450 400 Counts Acetic Acid 350 Conjugate Base 300 250 500 700 900 1100 1300 1500 1700 Wavelength (nm)
  15. 15. Acid-Base Results What does the spectrogram tell us?   C-O- peak is red-shifted by ~400cm-1 from the C-OH peak What does the red-shift mean?   Electron density has shifted  Bond vibration frequency is less
  16. 16. Acid-Base Results Acetic Acid Acetate Ion
  17. 17. Water-Ethanol Systems Liquid Ethanol   Forms straight chain layers  Held together by hydrogen bonding  Extremely hygroscopic
  18. 18. Water-Ethanol Systems Liquid Water   Forms a lattice structure  Held together by hydrogen bonding
  19. 19. Water-Ethanol Systems Water and ethanol form different liquid  structures What happens when water is added to  ethanol?  Water forms hydrogen bonds with ethanol  Structure of liquid ethanol is broken up
  20. 20. Water-Ethanol Experimental Five different water-ethanol solutions   20% ethanol to 100% ethanol Ethanol-Water System 800 750 700 650 600 100% Counts 550 80% 500 60% 40% 450 20% 400 350 300 500 700 900 1100 1300 1500 1700 Wavelength (nm)
  21. 21. Water-Ethanol Results The more water present, the more blue-  shifted the peaks  Peak shifts are linear with respect to amount of water added ~50cm-1 overall 
  22. 22. Future Directions Tip-enhanced Raman Spectroscopy   Chemical surface analysis  Non-destructive  AFM tip
  23. 23. Summary Raman spectroscopy provides insight into  molecular vibrational spectrum  Molecular Identification  Aqueous systems Experimental   Acid-Base ○ Stokes shifting was observed due to deprotonation  Ethanol-Water ○ Anti-Stokes shifting was observed due to disruption of ethanol liquid structure
  24. 24. References Purohit, Vishwas. quot;Sir C.V.Raman and Raman Spectroscopy (1888-1970).quot;  Buzzle.com. 1 Apr. 2005. 19 Apr. 2009 <http://www.buzzle.com/editorials/4-1-2005- 67909.asp>. Chumanov, George. “Raman Scattering Spectroscopy”. CH 412. Clemson University.  http://www.mhhe.com/physsci/chemistry/carey/  Yeo, Boon-Siang, Johannes Stradler, Thomas Schmid, Renato Zenobi, and Weihua  Zhang. quot;Tip-enhanced Raman Spectroscopy - Its status, challenges, and Future Directions.quot; Chemical Physics Letters 472 (2009): 1-13. ScienceDIrect. 6 Apr. 2009. 22 Apr. 2009 <http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TFN- 4VKP424- 9&_user=590719&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C00003019 8&_version=1&_urlVersion=0&_userid=590719&md5=bce1231e5c1255f84c11dce4025 8933c>.

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