Raman Spectroscopy
-
Upload
yomology -
Category
Technology
-
view
10.370 -
download
1
Transcript of Raman Spectroscopy
RAMAN SPECTROSCOPY
Matt Bloodgood
David Watts
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
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)
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).
What is Raman Scattering? Scattering of incident light – inelastic Rayleigh vs. Raman scattering
Figure 2. Jablonski Diagram of Rayleigh and Raman Scattering. (Chumanov 5)
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)
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
Spectrometer details
Raman Data
Data presented relative to excitation frequency.
Wavelength frequency (cm-1) Example:
Raman Spectroscopy Experiments Acid-Base
Objective: To analyze vibrational shift caused by hydrogen extraction using Raman spectroscopy
Water-Ethanol SystemsObjective: To analyze the effect on Raman
scattering of different water-ethanol solutions
Highly Qualitative
Acid-Base Experimental
Glacial Acetic Acid
OH- was used to deprotonate Acetic Acid
Acetate Ion
Acetic Acid Spectrogram
500 700 900 1100 1300 1500 1700250
300
350
400
450
500
Acetic Acid (CH3COOH)
Wavelength (nm)
Co
un
ts
Acetate Spectrogram
500 700 900 1100 1300 1500 1700250
300
350
400
450
500
Conjugate Base (CH3COO-)
Wavelength (nm)
Co
un
ts
Acid Base Overlay
500 700 900 1100 1300 1500 1700250
300
350
400
450
500
Acetic Acid – Acetate Overlay
Acetic Acid
Conjugate Base
Wavelength (nm)
Co
un
ts
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 shiftedBond vibration frequency is less
Acid-Base Results
Acetic Acid Acetate Ion
Water-Ethanol Systems
Liquid EthanolForms straight chain layersHeld together by hydrogen bondingExtremely hygroscopic
Water-Ethanol Systems
Liquid WaterForms a lattice structureHeld together by hydrogen bonding
Water-Ethanol Systems
Water and ethanol form different liquid structures
What happens when water is added to ethanol?Water forms hydrogen bonds with ethanolStructure of liquid ethanol is broken up
Water-Ethanol Experimental Five different water-ethanol solutions
20% ethanol to 100% ethanol
500 700 900 1100 1300 1500 1700300
350
400
450
500
550
600
650
700
750
800
Ethanol-Water System
100%
80%
60%
40%
20%
Wavelength (nm)
Co
un
ts
Water-Ethanol Results
The more water present, the more blue-shifted the peaksPeak shifts are linear with respect to amount
of water added
~50cm-1 overall
Future Directions
Tip-enhanced Raman SpectroscopyChemical surface analysisNon-destructiveAFM tip
Summary Raman spectroscopy provides insight into
molecular vibrational spectrumMolecular IdentificationAqueous systems
ExperimentalAcid-Base
○ Stokes shifting was observed due to deprotonationEthanol-Water
○ Anti-Stokes shifting was observed due to disruption of ethanol liquid structure
References 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>.
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. "Tip-enhanced Raman Spectroscopy - Its status, challenges, and Future Directions." 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=C000030198&_version=1&_urlVersion=0&_userid=590719&md5=bce1231e5c1255f84c11dce40258933c>.