Presented By
FAHAD AZIZ

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What is Spectroscopy?
 The study of how 'species' (i.e., atoms, molecules, solutions) react to light. Some studies depend on how much light an atom absorbs. The electromagnetic radiation absorbed, emitted or scattered by the molecule is analyzed. Typically, a beam of radiation from a source such as a laser is passed through a sample, and the radiation exiting the sample is measured. Some, like Raman, depend on a molecule's vibrations in reaction to the light.
 Sir Chandrashekhara Venkata Raman
 November 7, 1888-November 21, 1970
 Won the Noble Prize in 1930 for Physics
 Discovered the "Raman Effect"
 Besides Discovering the Raman Effect, He studied extensively in X-Ray Diffractions, Acoustics, Optics, Dielectrics, Ultrasonics, Photo electricity, and colloidal particles.
History of Raman Spectroscopy
 In 1928, Sir C.V. Raman discovered that radiation scattered by materials had an inelastic component.
 Only 1 in 1,000,000 (0.0001%) photons are scattered inelastically.
 By the 1930s, Raman had become the principal means of non-destructive chemical analysis.
 After WWII, advances in electronics and detectors allowed IR to surpass Raman in this role.
 Advent of lasers in the 1960s revived interest in Raman to some extent.
 In 1986, the first commercial FT-Raman instrument became available.
 In the late 1980s, notch filters improved the viability of Raman spectra.
 1980s and 1990s, dispersive Raman technology improved including the development of holographic instruments, refinement of triple spectrographs, etc.
 In 1992, the first holographic transmission grating is introduced.
 In 1993, the first 532-nm Raman spectrometer based on volume holographics is introduced.
 First KOSI on-line system is introduced in 1994.
 In 1996, the first non-contact fiber optic probe is introduced.
What is the Raman Effect?
What is Raman Spectroscopy?
Stokes Scattering
 Stokes scattering is, by convention, positive-shifted Raman scatter. Most Analytical work is done in this region.
 Represents inelastic scattering to a region of lower energy. This means that the energy of the detected radiation is higher in wavelength relative to the laser.
 The scattered spectrum appears similar to an IR spectrum and is interpreted similarly.
 The Principle of Mutual Exclusion often makes Raman spectrum complementary to the IR spectrum.
Rayleigh and Anti-Stokes Scattering
 Rayleigh scatter is the elastic scatter, i.e. same wavelength, as the incident laser. It is filtered and is excluded from the spectrum.
 Anti-Stokes scattering is inelastic scattering to a region of higher energy. This means that the energy of the detected radiation is lower in wavelength relative to the laser (therefore, higher frequency). By convention, it represents a negative Raman shift.
 The scattered spectrum is the mirror image to the spectrum from the Stokes scatter but is less intense. Therefore, only the more intense Raman bands are seen in the Anti-Stokes spectrum.
SERS vs. Raman
 During charge transfer, some vibrations will be altered due to a molecule's interaction with the surface, resulting in some of the SER bands being shifted in respect to the normal Raman Spectrum. SER spectra of a different small peptides and proteins were obtained from a roughened surface using a Raman spectrometer.
Why Raman?
 In Raman spectroscopy, by varying the frequency of the radiation, a spectrum can be produced, showing the intensity of the exiting radiation for each frequency. This spectrum will show which frequencies of radiation have been absorbed by the molecule to raise it to higher vibrational energy states.
What Exactly Is Being Measured?
Stokes vs. Anti Stokes
 Atoms are at a certain energy level at any given time.
 As a laser light hits the atom, it is excited and reaches a higher level of energy, and then is brought back down.
 If an atom is at a given energy level, it can be excited then fall below the original level.
 Anti-stokes spectrum are mirror spectrums of Stokes Raman Spectrums
 Using Stokes/Peaks to Determine Vibrations
 Raman Instruments
 Raman Spectroscopy: Summary