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Lecture 15

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chichi's version from 2018-05-01 14:19

Section 1

Question Answer
3 Components of Raman Instrument A laser source, a sample illumination system and a suitable spectrometer
Source of Ramannearly always lasers because their high intensity is necessary to produce Raman scattering of sufficient intensity to be measured with a reasonable signal-to-noise ratio. Because the intensity of Raman scattering varies as the fourth power of the frequency, argon and krypton ion sources that emit in the blue and green region of the spectrum have and advantage over the other sources
Argon ion wavelength488.0 or 514.5
Krypton ion wavelength530.9 or 647.1
Helium-neon wavelength632.8
Diode wavelength785 or 830
Nd-YAG wavelength1064
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Section 2

Question Answer
Sample Illumination System #1Sample handling for Raman spectroscopic measurements is simpler than for infrared spectroscopy because glass can be used for windows, lenses, and other optical components instead of the more fragile and atmospherically less stable crystalline halides
Sample Illumination System #2In addition, the laser sources is easily focused on a small sample area and the emitted radiation efficiently focused on a slit. Consequently, very small samples can be investigated. A common sample holder for non-absorbing liquid samples is an ordinary glass melting-point capillary
Liquid samples:A major advantage of sample handling in Raman spectroscopy compared with infrared arises because water is a weak Raman scatterer but a strong absorber of infrared radiation. Thus, aqueous solutions can be studied by Raman spectroscopy but not by infrared. This advantage is particularly important for biological and inorganic systems and in studies dealing with water pollution problems
Solid samples:Raman spectra of solid samples are often acquired by filling a small cavity with the sample after it has been ground to a fine powder. Polymers can usually be examined directly with no sample pretreatment
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Section 3

Question Answer
Raman spectrometers were similar in design and used the same type of components as the classical______________-ultraviolet-visible dispersing instruments
Why is Raman often superior to infrared? #1It's superior due to investigating inorganic systems because aqueous solutions can be employed
Why is Raman often superior to infrared? #2In addition, the vibrational energies of metal-ligand bonds are generally in the range of 100 to 700 cm^-1, a region of the infrared that is experimentally difficult to study
Raman studiesare potentially useful sources of information concerning the composition, structure, and stability of coordination compounds
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Section 4

Question Answer
Raman Spectra of Organic SpeciesRaman Spectra are similar to infrared spectra in that they have regions that are useful for functional group detection and fingerprint regions that permit the identification of specific compounds. Raman spectra yield more information about certain types of organic compounds than do their infrared counterparts
Biological Applications of Raman SpectoscopyRaman spectroscopy has been applied widely for the study of biological systems. The advantages of this technique include the small sample requirement, the minimal sensitivity toward interference by water, the spectral detail, and the conformational and environmental sensitivity
Quantitative Applications #1Raman spectra tend to be less cluttered with peaks than infrared spectra. As a consequence, peak overlap in mixtures is less likely, and quantitative measurements are simpler. In addition, Raman sampling devices are not subject to attack by moisture, and small amounts of water in a sample do not interfere.
Quantitative Applications #2Despite these advantages, Raman spectroscopy has not yet been exploited widely for quantitative analysis. This lack of use has been due largely to the rather high cost of Raman spectrometers relative to that of absorption instrumentation
RBM bandsRadial Breathing Modes
RBM bands good forGood indicator of diameter of tube
Wavelength of RBMTypically 400-100 cm^-1
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Section 5

Question Answer
Raman spectroscopy is a powerful tool for a wide range of chemical analysesContaminant analysis; inorganic materials; component distribution and quantification by mapping; Especially useful for high-throughput automated applications
FT-RamanBest choice to minimize fluorescence
Dispersive Macro RamanExcellent choice for identification and QA/QC applications
Dispersive Micro RamanBest choice for small particles; excellent spatial resolution
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