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

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Acetic Acid (CH3COOH)

Wavelength (nm)

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Acetate Spectrogram

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Conjugate Base (CH3COO-)

Wavelength (nm)

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Acid Base Overlay

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Acetic Acid – Acetate Overlay

Acetic Acid

Conjugate Base

Wavelength (nm)

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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

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Ethanol-Water System

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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>.