EXAFS spectra absorption fine structure spectroscopy

Extended X-ray absorption fine structure (EXAFS) spectrum Part of an X-ray absorption spectrum that is used to identify the coordination of atoms, estimate bond lengths, and determine the adsorption complexes on the surfaces of adsorbents. EXAFS spectra may provide useful information on the speciation (valence state), surface complexes, and the coordination of arsenic on adsorbents (e.g. (Randall, Sherman and Ragnarsdottir, 2001 Ladeira, et al. (2001) Teixeira and Ciminelli (2005) Kober, et al. (2005)) (compare with X-ray absorption spectroscopy (XAS), X-ray absorption near edge structure (XANES) spectra, and X-ray absorption fine structure spectroscopy (XAFS)). 

NEXAFS — Near-edge extended X-ray absorption fine structure (spectroscopy), evaluation of the X-ray absorption spectrum around and slightly below the absorption edge, for details see - EXAFS. 

EXAFS is part of the field of X-ray absorption spectroscopy (XAS), in which a number of acronyms abound. An X-ray absorption spectrum contains EXAFS data as well as the X-ray absorption near-edge structure, XANES (alternatively called the near-edge X-ray absorption fine structure, NEXAFS). The combination of XANES (NEXAFS) and EXAFS is commonly referred to as X-ray absorption fine structure, or XAFS. In applications of EXAFS to surface science, the acronym SEXAFS, for surface-EXAFS, is used. The principles and analysis of EXAFS and SEXAFS are the same. See the article following this one for a discussion of SEXAFS and NEXAFS. 

Figure 1.1 The electiomagnetic spectrum, showing the different microscopic excitation sources and the spectroscopies related to the different spectral regions. XRF, X-Ray Fluorescence AEFS, Absorption Edge Fine Structure EXAFS, Extended X-ray Absorption Fine Structure NMR, Nuclear Magnetic Resonance EPR, Electron Paramagnetic Resonance. The shaded region indicates the optical range.

A non exhaustive description of the history of X-ray Absorption Spectroscopy (XAS) can be found in Ref. 1. The modem EXAFS (Extended X-ray Absorption Fine Structure) technique began in the early seventies of the last century. It corresponds to the concomitance of both theoretical and experimental developments. Between 1969 and 1975, Stem, Sayers and Lytle succeeded in interpreting theoretically the X-ray Absorption Structures observed above an absorption edge [2], while during the same period, the advent of synchrotron radiation (SR) sources reduced drastically the acquisition time of a spectrum if compared to data obtained with conventional X-ray tubes. XAS provides essential information about the local atomic geometry and the electronic and chemical state of a specific atom, for almost any element of the periodic table (Z>5). This prime tool for... 

Multinuclear NMR- ( C, Pt, T1), 1R-, Raman-spectroscopy. Electron Spectroscopy for Chemical Analysis (ESCA), X-ray, and Extended X-ray Absorption Fine Structure (EXAFS) studies confirm direct, short (2.60-2.64 A) Pt-Tl bonds. Figure 1. shows a typical ° T1 NMR spectrum of [(N C)5Pt-Tl( CN)] together with the structure determined by EXAFS. The spin-spin coupling pattern is consistent with 4 -h 1 - -1 equivalentligands (I = 1/2), respectively and one Pt nucleus (natural abundance 33.8%, 1=1 /2). The spectrum has been selected to illustrate the usefulness of T1 NMR spectroscopy in studies of the inorganic chemistry of thallium. The compounds are diamagnetic, and... 

X-ray absorption spectroscopy is a powerful tool for nanoparticle analysis due to its selectivity and independence of sample physical state. It is limited in range to the region within about 0.5-0.7 nm of a particular (chosen) absorber atom in the structure, but can be applied to amorphous or even liquid samples. The basic theory behind the origins and analysis of the extended X-ray absorption fine structure (EXAFS) has been well described by Sayers et al. (1970, 1971) and Lee et al. (1981). with mineralogical applications detailed by Brown et al. (1988). The crucial aspect of the EXAFS spectrum is that it is formed by an electron backscattering process in the vicinity of the absorber... 

X-ray absorption spectroscopy is a powerful method to assess the structure of mercury thiolate complexes. X-ray Absorption Near Edge Structure (XANES) spectroscopy can cleanly differentiate Hg(0), Hg(I) and Hg(II) by the energy of the emission edge. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy provides information regarding the coordination number and Hg-S bond distances. Typically, the EXAFS spectrum can establish the coordination number (/.e., number of sulfur atoms) to within 20%. More important, the bond length precision is 0.01 A. Given that each increase of one... 

Experimental absorption spectrum measured over the V K-edge indicating the relevant energy regions for X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy... 

FIGURE 7.14 X-ray absorption spectroscopy (XAS) spectrum of arsenate with the x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) regions indicated. (Reprinted from Luo, L., and S. Zhang, Sci. China Chem. 53, 12, 2529-2538, 2010. With permission from Science China Press.)... 

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