Bound rays absorption

X-ray absorption spectroscopy combining x-ray absorption near edge fine structure (XANES) and extended x-ray absorption fine structure (EXAFS) was used to extensively characterize Pt on Cabosll catalysts. XANES Is the result of electron transitions to bound states of the absorbing atom and thereby maps the symmetry - selected empty manifold of electron states. It Is sensitive to the electronic configuration of the absorbing atom. When the photoelectron has sufficient kinetic energy to be ejected from the atom It can be backscattered by neighboring atoms. The quantum Interference of the Initial... 

Bacteria and their composites with soil minerals or organic matter are capable of taking up a wide range and variety of toxic metals in soil environments. Research done over the last decade or so has greatly improved our understanding of the mechanisms on biosorption of metals and bacte-ria-metal-soil component interactions. However, more studies from molecular level are needed in order to enhance the ability of bacteria and their association with soil components to remediate toxic metals-contaminated soils. The focus of future investigations should be on the mechanisms by which metals are sorbed and bound by bacterial cell surfaces and bacteria-soil/mineral composites. In this connection, X-ray absorption spectroscopy (XAS) is a promising technique because it can provide information about... 

A Sulfur K Edge X-ray Absorption Near Edge Structure (XANES) Spectroscopy method has been developed for the direct determination and quantification of the forms of organically bound sulfur in nonvolatile petroleum and coal samples. XANES spectra were taken of a number of model compounds, mixtures of model compounds, heavy petroleum and coal samples. Analysis of the third derivatives of these spectra allowed approximate quantification of the sulfidic and thiophenic components of the model mixtures and of heavy petroleum and coal samples. These results are compared with those obtained by X-ray Photoelectron Spectroscopy (XPS). 

In the crystal structure of PCDase, the iron has trigonal bipyramidal pentacoordination with one water ligand. Recent extended X-ray absorption fine structure (EXAFS) studies indicate that the bound water is more... 

Xia, K., Bleam, W., and Helmke, P. A. (19976). Studies of the nature of binding sites of first row transition elements bound to aquatic and soil humic substances using X-ray absorption spectroscopy. Geochim. Cosmochim. Acta 61, 2223-35. 

The X-ray absorption spectra of a series of 28 model Fem complexes and those of ovatransferrin, protocatechuate 3,4-dioxygenase and catechol 1,2-dioxygenase have been analyzed, and appear to give information on the coordination number of the protein-bound iron. Thus the transferrin complexes appear to be six- or seven-coordinate, while the dioxygenase complexes could be five-or six-coordinate.816... 

Some researchers have doubted whether nonporphyrin metal compounds exist at all in petroleum (Goulon et al., 1984 Berthe et al., 1984). This speculation is based on the similarities in spectral features of petroleum-bound metals and model-metal porphyrin compounds from selected petroleums under the examination of x-ray absorption, photoelectron, and laser desorption spectroscopies. Interpretation of spectra from these methods, however, is uncertain and difficult given the lack of sufficient data on model compounds, particularly nonporphyrin metals and in a petroleum environment or matrix. 

Biomass may also sorb As(III) from water. Teixeira and Ciminelli (2005) removed considerable As(III) with ground chicken feathers treated with ammonium thioglycolate. X-ray absorption near edge structure (XANES) spectra indicate that the adsorbed arsenic is still in the +3 valence state and that each atom is bound to three sulfur atoms associated with reduced cysteine amino acids (HC>2CCH(NH2)CH2SH) in the feathers. At pH 5 and biomass dosages of 2.0gL 1, the sorption capacity of the material was as high as 0.265 mmol As(III) g-1 biomass (19.9 mg As(III) g-1 biomass Table 7.2). The presence of 0.01 mol L-1 of phosphate had only minor effects on the sorption capacity, which was 0.260 mmol As(III) g 1 biomass (19.5 mg As(III) g-1 biomass) (Teixeira and Ciminelli, 2005, 898). 

Atoms are not rigidly bound to the lattice, but rather vibrate around their equilibrium positions. If we were able to examine the crystal over a very brief observation time, we would see a slightly disordered lattice. Incident electrons see these deviations, and this is for example the reason that in low-energy electron diffraction (LEED) the spot intensities of diffracted beams depend on temperature. At high temperatures the atoms deviate more from their equilibrium position than at low temperatures, and a considerable number of atoms is not at the equilibrium position necessary for diffraction. Thus, spot intensities are low and the diffuse background high. Similar considerations apply in other scattering techniques, as well as in extended X-ray absorption fine structure (EXAFS) and in Mossbauer spectroscopy. 

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