Brief explanation

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Raman Spectroscopy

2. Table Contents
• Definition
• Introduction
• The Raman Effect
• How does Raman Spectroscopy work?
• Applications of Raman Spectroscopy
• Information provided by Raman spectroscopy
• Conclusion
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3. Definition
Raman spectroscopy
belongs into the category of
vibrational spectroscopy.
This means that it analyzes a
sample chemically, by using
light to create (excite)
molecular vibration, and
interpreting this interaction
afterwards.
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4. Introduction
• It is based on the inelastic scattering of light that occurs
when matter is irradiated by light. As the change of
wavelength is very small compared to the wavelength of the
irradiating light, the change of wavelength is most easily
observed when using monochromatic light sources.
• After this (monochromatic) light has interacted with the
sample, a very small part of it has changed its wavelength.
This is change is called: the Raman effect. We can now
collect that light and can use it gain information about the
sample.
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5. • For a better understanding it is important to know, that when
photons (light) "strike" matter, most of the scattered light
remains unchanged in its wavelength.
• For example, if you point a green laser pointer at a wall, you
will always see a green dot. The scattered light obviously has
the same color and this phenomenon is called Rayleigh
scattering.
• However, also inelastic scattering processes can occur, which
then lead to the emission of light with a different wavelength.
This usually happens in relation to molecular vibration. This
scattering phenomenon, which was predicted by Adolf Smekal
in 1923 and discovered by C.V. Raman in 1930, is called the
Raman effect. ●●●
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The Raman effect

6. The Raman effect
• Discovering and understanding the Raman effect opened
the door to a new kind of spectroscopy. However, Raman
spectroscopy did not really take off until the discovery of
the laser, since the use of monochromatic light plays an
important role.
• Thus, the sample is irradiated with a laser and some of
the scattered light is analyzed with a spectrograph
(dispersive or FT technology). At the end we obtain a
Raman spectrum that shows us characteristic signals or
"bands" for the material under investigation.
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7. •To acquire Raman spectra, you just have to focus the laser onto
the sample you want to investigate. That sample however, must
not be showing fluorescence to the laser used for excitation.
•If that is the case, the fluorescence will cover most of the
Raman effect, since it is so weak in comparison.
•After the laser light has irradiated the sample, the scattered light
is passed through a filter (to get rid of any light from the
excitation laser).
•Then it is directed onto a grating, which distributes the inelastic
parts like a prism and according to wavelength. At the end these
rays are directed to a CCD sensor which then outputs a spectrum
depending on the intensity.
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How does Raman spectroscopy work?

8. Raman spectroscopy can be used in all areas where
non-destructive (microscopic) chemical analysis and
imaging is required. It delivers answers for qualitative
and quantitative analytical questions.
In general, Raman is easy to use and quickly provides
key information to characterize the chemical
composition and structure of a sample. Basically, it
matters little whether the samples are solid, liquid or
gaseous.
●●●
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Applications of Raman spectroscopy

9. Applications of Raman spectroscopy
Here are some applications of Raman spectroscopy:
• Pharmaceuticals
• Geology and mineralogy
• Semiconductors
• Material research
• Life-science
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10. A Raman spectrum is like a chemical fingerprint that clearly
identifies a molecule or material. And just like a human
fingerprint, it can be compared with reference libraries to
identify the material very quickly or distinguish it from others.
Such Raman spectral libraries often contain hundreds of spectra
with which the spectrum of a sample is compared to determine
the analyte.
It provides insights into a sample's:
• Chemical composition and properties
• Crystallinity and polymorphism
• Contaminations and defects
• Thermal and mechanical exposure
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Information provided by Raman spectroscopy

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12. Conclusion
• Raman spectroscopy is a powerful tool to assess
internal quality and safety, due to many advantages
such as non destructive detection, no sample
preparation, and fast measurement. Due to its
narrow and sharply resolved bands,
• Raman spectroscopy shows great potential in
qualitative, structural, and quantitative analysis. The
industrial application of this technology may be a
realistic option in the near future.
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13. References
 Google.com
 Wikipedia.org
 Studymafia.org
 Slidespanda.com

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