1. Matt Bloodgood
David Watts

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. 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. 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. 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. 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. 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. Spectrometer details

9. Raman Data
Data presented relative to excitation

frequency.
 Wavelength  frequency (cm-1)
 Example:

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. Acid-Base Experimental
Glacial Acetic Acid

OH- was used to deprotonate Acetic

Acid
Acetate Ion

12. Acetic Acid Spectrogram
Acetic Acid (CH3COOH)
500
450
400
Counts
350
300
250
500 700 900 1100 1300 1500 1700
Wavelength (nm)

13. Acetate Spectrogram
Conjugate Base (CH3COO-)
500
450
400
Counts
350
300
250
500 700 900 1100 1300 1500 1700
Wavelength (nm)

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. 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. Acid-Base Results
Acetic Acid Acetate Ion

17. Water-Ethanol Systems
Liquid Ethanol

 Forms straight chain layers
 Held together by hydrogen bonding
 Extremely hygroscopic

18. Water-Ethanol Systems
Liquid Water

 Forms a lattice structure
 Held together by hydrogen bonding

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. 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. 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. Future Directions
Tip-enhanced Raman Spectroscopy

 Chemical surface analysis
 Non-destructive
 AFM tip

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. 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>.