X-ray and Related Spectroscopic Techniques

Clement R. Yonker, John C. Lineman and John L. Fulton 

The techniques described in Chapters 3.1 and 3.2 provide information on a molecular level about solute structure, solution dynamics and chemistries in SCFs. The goal of this chapter is to briefly discuss other spectroscopic techniques applied to SCFs which can be used to determine solution structure or the effects of pressure and temperature on reactions in these solvent systems. An overview of this type, by its nature, can not be considered inclusive, but it is hoped to give future practitioners in the field a reasonable expectation of the type of molecular-level information that different spectroscopic techniques provide under SCF conditions. 

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YonkerCR, Linehan JC, Fulton JL. UV, EPR, X-ray and related spectroscopic techniques. In Jessop PG, Leitner W, eds. Chemical Synthesis Using Supercritical Fluids. Weinheim, Germany Wiley-VCH, 1999 195-212. 

K2FeSi308 (Waychunas et al., 1988). The EXAFS spectra of the melts along with certain model compounds and a quenched glass are shown in Fig. 8.11. There is no doubt that such direct studies of melts by x-ray absorption and related spectroscopic methods are the techniques of the future. 

The mechanism of the activation of H2O2 by TS-1 and related catalysts has been the subject of much research using spectroscopic and computational techniques. This has centred on the nature of the active site and its mode of reaction with H2O2, solvents and the organic substrates. Work to elucidate the structure of the active site has concentrated on the coordination chemistry of the titanium. X-ray and neutron diffraction studies, coupled with X-ray absorption, infrared and Raman spectroscopies, give evidence that most of the Ti(IV) in calcined TS-1, in the absence of any adsorbate molecules, is in tetrahedral coordination. Upon addition of one molecule of water, one of the Ti-OSi bonds is hydrolysed and the titanium adopts tetrahedral coordination as Ti(0Si)30H. Addition of a further water molecule gives rise to a pentaco-ordinated titanium. ... 

In this chapter, the application of various spectroscopic, chromatographic, X-ray and microscopic techniques to the analysis and characterization of HPOPs will be presented. In so doing, however, it must be stressed that because of sheer space limitations it would be impractical to cover all aspects of the methods currently used to analyze, identify and characterize today s pigment products and related materials. Mention should therefore be made of the following fourteen techniques, which are not discussed in detail here but are all in use today in pigments laboratories and are worthy of further study. 

Structural investigations into the degree of branching and into the position and nature of glycosidic bonds and of non-carbohydrate residues in polysaccharides may include periodate oxidation and other procedures such as exhaustive methylation. X-ray diffraction and spectroscopic techniques such as nuclear magnetic resonance and optical rotatory dispersion also give valuable information especially relating to the three-dimensional structures of these polymers. 

Some instrumental methods have been used for the investigation of sulphide mineral-thio-collector system such as infra-red (IR) spectroscopy (Mielezarski and Yoon, 1989 Leppinen et al., 1989 Persson et al, 1991 Laajalehto et al, 1993 Zhang., et al., 2004a) and X-ray photoelectron spectroscopy (XPS) (Pillai et al, 1983 Page and Hazell, 1989 Grano et al, 1990 Laajalechto et al, 1991). These surface sensitive spectroscopic techniques can be applied for the direct determination of the surface composition at the conditions related to flotation. 

A number of ex situ spectroscopic techniques, multinuclear NMR, IR, EXAFS, UV-vis, have contributed to rationalise the overall mechanism of the copolymerisation as well as specific aspects related to the nature of the unsaturated monomer (ethene, 1-alkenes, vinyl aromatics, cyclic alkenes, allenes). Valuable information on the initiation, propagation and termination steps has been provided by end-group analysis of the polyketone products, by labelling experiments of the catalyst precursors and solvents either with deuterated compounds or with easily identifiable functional groups, by X-ray diffraction analysis of precursors, model compounds and products, and by kinetic and thermodynamic studies of model reactions. The structure of some catalysis resting states and several catalyst deactivation paths have been traced. There is little doubt, however, that the most spectacular mechanistic breakthroughs have been obtained from in situ spectroscopic studies. 

Fullerene compounds have been characterized by typical spectroscopic techniques including 13C NMR, IR, UV-vis, electrochemical methods, mass spectrometry (MS), and X-ray diffraction. Each of these methods is discussed here in relation to specific points arising from the... 

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