Spectrometry Raman

Not all molecules are in the ground vibrational state. A few molecules are in the first excited state of each vibrational mode, u, = 1. Neglecting the effect of degeneracy, the Boltzmann population of molecules in the first vibrational state of the ith mode is given by 

The intensity of bands in the Raman spectrum of a compound are governed by the change in polarizability, a, that occurs during the vibration. The intensity of any band in the Raman spectrum is given by the following expression  

There are many reasons why scientists want to measure the Raman spectra of compounds. First, many bands that are weak in the infrared spectrum are among the strongest bands in the Raman spectrum. For example, the S—S and C=C stretching bands are often so weak as to be essentially unrecognizable in the IR spectrum but stick out like the proverbial sore thumb in a Raman spectmm. Second, some Raman bands are found at very characteristic frequencies. For instance, monosubstituted aromatic compounds, together with 1,3-disubstituted and 1,3,5-trisubstituted aromatics, have a very intense band at 1000 cm. This band, along with the presence or absence 

For these reasons, analytical Raman spectrometry has undergone a remarkable rebirth since about 1985. Instruments based on Fourier transform techniques and CCD array detectors are commercially available from a large number of vendors in North America, Europe, and Asia. Like infrared spectrometry, Raman spectrometry has outlived its seventh age, although whether it has matured through its second childhood yet is debatable. Nonetheless, Raman spectrometry is still a vital weapon in a vibrational spectroscopist s arsenal. 

In Chapters 2 to 8 we describe the theory and instrumentation needed for an appreciation of the way that Fourier transform infrared and Raman spectra are measured today. The sampling techniques for and applications of FT-Raman spectrometry are described in Chapter 18. The remaining chapters cover the techniques and applications of absorption, reflection, emission, and photoacoustic spectrometry in the mid- and near-infrared spectral regions. 

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Raman scattering cell Raman spectrometry Raman spectroscopy... 

Raman spectrometry is another variant which has become important. To quote one expert (Purcell 1993), In 1928, the Indian physicist C.V. Raman (later the first Indian Nobel prizewinner) reported the discovery of frequency-shifted lines in the scattered light of transparent substances. The shifted lines, Raman announced, were independent of the exciting radiation and characteristic of the sample itself. It appears that Raman was motivated by a passion to understand the deep blue colour of the Mediterranean. The many uses of this technique include examination of polymers and of silicon for microcircuits (using an exciting wavelength to which silicon is transparent). 

Alak AM, Vo-Dinh T. 1987. Surface-enhanced raman spectrometry of organophosphorus chemical agents. Anal Chem 59 2149-2153. 

Applications Sollinger and Sawatzki [793] have reported the use of TLC-Raman for routine applications, e.g. TLC of hydroxybenzenes (including hydro-quinone and pyrogallol) on conventional, silica gel and specific Raman-TLC plates (coated with spherical silica gel). Databases were used for identification of substances. Typical detection limits were in the low p,g region per application, Micro-Raman spectrometry has been employed in analysing TLC fractions from polymer additives within a detection limit... 

In polymer/additive deformulation (of extracts, solutions and in-polymer), spectroscopic methods (nowadays mainly UV, IR and to a lesser extent NMR followed at a large distance by Raman) play an important role, and even more so in process analysis, where the time-consuming chromatographic techniques are less favoured. Some methods, as NMR and Raman spectrometry, were once relatively insensitive, but seem poised to become better performing. Quantitative polymer/additive analysis may benefit from more extensive use of 600-800 MHz 1-NMR equipped with a high-temperature accessory (soluble additives only). 

Also known for some time is a phase transition at low temperature (111K), observed in studies with various methods (NQR, elasticity measurement by ultrasound, Raman spectrometry) 112 temperature-dependent neutron diffraction showed the phase transition to be caused by an antiphase rotation of adjacent anions around the threefold axis ([111] in the cubic cell) and to lower the symmetry from cubic to rhombohedral (Ric). As shown by inelastic neutron scattering, this phase transition is driven by a low-frequency rotatory soft mode (0.288 THz 9.61 cm / 298 K) 113 a more recent NQR study revealed a small hysteresis and hence first-order character of this transition.114 This rhombohedral structure is adopted by Rb2Hg(CN)4 already at room temperature (rav(Hg—C) 218.6, rav(C—N) 114.0 pm for two independent cyano groups), and the analogous phase transition to the cubic structure occurs at 398 K.115... 

CARS Coherent Anti-Stokes Raman Spectrometry... 

Lewis I.R., Griffiths P.R., Raman Spectrometry with Fiber-Optic Sampling, Appl. Spectrosc., 1996 50 (10) 12A - 30A. 

Vo-Dinh T., Hiromoto M.Y.K., Begun G.M., Moody R. L., Surface-enhanced Raman spectrometry for trace organic-analysis, Anal. Chem. 1984 56 1667-1670. 

Vo-Dinh T., Surface-Enhanced Raman Spectrometry, in Chemical Analysis of Polycyclic Aromatic Compounds, Vo-Dinh T. ed., Wiley, New York (1989). 

Pemberton J.E., Buck R.P., Detection of low concentrations of a colored adsorbate at silver by surface-enhanced and resonance-enhanced Raman spectrometry, Anal. Chem. 1981 53 2263-2267. 

Alak A.M., Vo-Dinh T., Surface-enhanced Raman spectrometry of chlorinated pesticides, Anal. Chim. Acta 1988 206 333-337. 

Enlow P.D., Buncick M., Warmack R.J., Vo-Dinh T., Detection of nitro polynuclear aromatic-compounds by surface- enhanced raman-spectrometry, Anal. Chem. 1986 58 1119-1123. 

Samson P.J., Fibre optic gas sensing using raman spectrometry, Proc. 14th Australian Conf. on Optical Fibre Technology, Brisbane, 1989, pp. 59-65. 

J.B. Slater, J.M. Tedesco, R.C. Fairchild and l.R. Lewis, Raman spectrometry and its adaptation to the indnstrial revolution, in Handbook of Raman Spectroscopy From the Research Laboratory to the Process Line, l.R. Lewis and H.G.M. Edwards (Eds), Practical Spectroscopy Series 28, Marcel Dekker, New York, 2001. 

M. Lopez-Sanchez, M.J. Ruedas-Rama, A. Ruiz-Medina, A. Molina-Diaz and M.J. Ayora-Canada, Pharmaceutical powders analysis using FT-Raman spectrometry Simultaneous determination of sulfathiazole and sulfanilamide, Talanta, 74, 1603-1607 (2008). 

Chevron Philhps Chemical Company LP, Raman spectrometry for monitoring and control of slurry processes for polymerizing olehns. Inventor D.R. Battiste. 20 Apr 2004. 11 pp. (inch 1 fig.). Appl. 3 Nov 2000. Int. Cl. C08F 2/14. US Patent Specification 6,723,804 B1... 

Gilbert, B., Chauvin, Y., and Guibard, L, Investigation by Raman spectrometry of a new room-temperature organochloroaluminate molten salt, Vtb. Spectrosc., 1, 299-304,1991. 

Adama Mickiewicza Poznaniu, Wydz. Mat., Fiz. Chem., Ser. Chem., 1975,18, 29-48. Study by Infrared and Raman Spectrometry of Molecular and Crystalline Structures of Some Nitrogen Heterocycles , A. Lautie, M. H. Limage and A. Novak, in Proceedings of the 18th Colloquium Spectroscopicum Internationale , 1975, vol. 2, pp. 430-434. 

Dimercury(I) n complexes are formed between aromatic compounds and Hg2(AsF6)2 in liquid S02 as solvent.113,121 Insoluble complexes with the ratio arene Hg2+ = 1 1 (arene = benzene, naphthalene, 2-methylnaphthalene, 2,6-dimethylnaphthalene, acenaphthene, fluor-anthrene, phenanthrene, anthracene, 9,10-dimethylanthracene or 1,3-dinitrobenzene) or 1 2 (arene = 9,10-benzophenanthrene) have been characterized by elemental analysis and, in some cases, by Raman spectrometry.113,120 The 13CNMR data allow the estimation of formation constants for the hexamethylbenzene, p-xylene and 1,4-dichlorobenzene complexes together with the chemical shifts for the bound substrates in these cases.121 Probably the coordination compounds of dimercury(I) salts with carbazole, dibenzofuran and diben-zothiophene are also n complexes.122... 

Like infrared spectrometry, Raman spectrometry is a method of determining modes of molecular motion, especially the vibrations, and their use in analysis is based on the specificity of these vibrations. The methods are predominantly applicable to die qualitative and quantitative analysis of covalently bonded molecules rather than to ionic structures. Nevertheless, they can give information about the lattice structure of ionic molecules in the crystalline state and about the internal covalent structure of complex ions and the ligand structure of coordination compounds both in the solid state and in solution. 

See also Spcctrochcmical Analysis (Visible) Spcctro Instruments Spectroscope and Raman Spectrometry. 

Jones, R. N., and C. Sandorfy The application of infrared and Raman spectrometry to the elucidation of molecular structure, in Technique of organic chemistry, Vol. IX, ed. W. West. New York Interscience Publishers, 1956. 

Gomushkin IB, Eagan PE, Novikov AB, Smith BW, Winefordner JD. Automatic correction of continuum background in laser-induced breakdown and Raman spectrometry. Applied Spectroscopy 2003, 57, 197-207. 

Keywords ion beam analysis, Raman spectrometry, archaeometry, PIXE, RBS, NRA, garnets... 

The following example is a illustration of how photon and charged particles techniques like the micro-PIXE and micro-Raman spectrometry can be combined to solve an important archaeological issue, namely to unveil the intriguing provenance of the red gemstones mounted on barbarian jewels from the early Middle-Ages [11]. 

The second provenance criterion is based on the identification of inclusions in gemstones. Micro-Raman spectrometry was used for this task in almandine garnets. Various inclusions were observed like apatite, zircon, monazite, calcite, and quartz and two of them, curved needles of sillimanite (Al2Si05) and 10-pm metamict radioactive crystals, were specifically found in archaeological garnets. Fig. 6 shows the Raman spectra of a sillimanite needle, which is a mineral formed under a high temperature and high pressure metamorphism. 

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