X-Ray Absorption Near Edge Spectroscopy XANES

X-ray absorption near-edge spectroscopy (XANES) suggests that, in most of the enzymes, the reduction to Ni-SI also implies a change in the coordination number of the Ni ion from 5 to 6 (74). 

Elder, R.C., Tepperman, K.G., Eidsness, M.K., Heeg, M.J., Shaw, C.F. Ill and Schaeffer, N. A. (1983) Gold-based antiarthritic drugs and metabolites. Extended x-ray adsorption fine structure (EXAFS) spectroscopy and x-ray absorption near edge spectroscopy (XANES). ACS Symposium Series, 209, 385-400. 

The most prevalent technique exploiting synchrotron radiation is X-ray absorption spectroscopy (XAS, also called X-ray absorption fine structure, XAFS). Two related types of experiments are conducted X-ray absorption near-edge spectroscopy (XANES), which probes the initial absorption edge and related nearby structure, and... 

Extended X-ray absorption fine structure (EXAFS) X-ray absorption near edge spectroscopy (XANES)... 

Extended X-ray absorption fine structure (EXAFS) on the other hand, is due to the interference of electron waves between atoms, and provides local structure information that is limited to a few interatomic distances. Here, we talk about the distance and the number of nearest and next-nearest neighbors of atoms in the catalyst. The more uniform the environment is through the catalyst, the more meaningful is the EXAFS information. Related to this method is X-ray absorption near edge spectroscopy (XANES), which deals with the detailed shape of the absorption edge, and yields important information on the chemical state of the absorbing atom. Commonly, one uses nowadays the acronym XAFS to include both EXAFS and XANES. 

Tossell, J. A., G. E. Brown, Jr., and G. A. Waychunas (1985a). Studies of the unoccupied molecular orbitals of tetrahedral oxyanions. TO/, and related molecules by x-ray absorption near edge spectroscopy (XANES) and multiple-scattering (MS) XoL molecular orbital calculations, GSA Ann. Meeting Ahst. 

XANES. - Au(CH3)2(acac)/MgO X-ray absorption, near edge spectroscopy (XANES) was used to determine the oxidation state of MgO-supported Au particles. These samples were prepared by decorating the surface of MgO with a Au(III) complex Au(CH3)2(acac). The samples were then analyzed for Au oxidation state as a function of the pretreatment gas (He or H2) and pretreatment method. With increasing temperature of treatment, in either He or H2, the Au was reduced from the cation to the metal. In the absence of H2, it was speculated... 

A variety of methods have been used to characterize the solubility-limiting radionuclide solids and the nature of sorbed species at the solid/water interface in experimental studies. Electron microscopy and standard X-ray diffraction techniques can be used to identify some of the solids from precipitation experiments. X-ray absorption spectroscopy (XAS) can be used to obtain structural information on solids and is particularly useful for investigating noncrystalline and polymeric actinide compounds that cannot be characterized by X-ray diffraction analysis (Silva and Nitsche, 1995). X-ray absorption near edge spectroscopy (XANES) can provide information about the oxidation state and local structure of actinides in solution, solids, or at the solution/ solid interface. For example, Bertsch et al. (1994) used this technique to investigate uranium speciation in soils and sediments at uranium processing facilities. Many of the surface spectroscopic techniques have been reviewed recently by Bertsch and Hunter (2001) and Brown et al. (1999). Specihc recent applications of the spectroscopic techniques to radionuclides are described by Runde et al. (2002b). Rai and co-workers have carried out a number of experimental studies of the solubility and speciation of plutonium, neptunium, americium, and uranium that illustrate combinations of various solution and spectroscopic techniques (Rai et al, 1980, 1997, 1998 Felmy et al, 1989, 1990 Xia et al., 2001). 

The structure of the copolymer, poly(di-n-butylstannane-co-methylphenylsilane) with a Sn Si ratio of 1 3 was determined with X-ray absorption fine-structure spectroscopy (EXAES) and X-ray absorption near-edge spectroscopy (XANES). The bond distances of Sn-Sn (2.82 A), Sn-Si (2.58 A), and Sn-C (2.15 A) in the copolymer were comparable with the cyclooligostannylsilane, illustrated in Eigure 3.8.1. 

A veritable arsenal of techniques has been mobilized to provide information regarding the structure of redox molecular sieves [9-14], X-Ray powder diffraction (XRD) provides an immediate check for crystallinity and structural type. X-Ray absorption fine structure spectroscopy (EXAFS) and X-ray absorption near edge spectroscopy (XANES) give fiirther insights into coordination geometry and bond lengths. Infiared and Raman spectroscopy have been used to identify characteristic features, e.g. the 960 cm bond attributed to the Si-OTi stretching vibration in TS-1 [9]. 

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