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  • 2000-2004  (6)
  • 1990-1994  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Structure of densified vitreous silica: Silicon and oxygen XANES spectra and multiple scattering calculations (1992)
    Springer
    Physics and chemistry of minerals 19 (1992), S. 171-175 
    Details
    ISSN: 1432-2021
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Abstract The decrease of the mean Si-O-Si angle in vitreous silica upon densification from 2.20 to 2.36 gcm-3 has been followed by oxygen and silicon K-edge XANES spectroscopy. Multiple scattering calculations using clusters of two shells around the oxygen and silicon atoms, respectively, are in good agreement with experimental absorption spectra and confirm mean Si-O-Si angles between 130 and 144° for these samples, and a decrease of the mean angle with densification. The experimental spectra also exhibit features due to scattering at outer (〉2) shells around the photoabsorbers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00202105
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  • 2
    Digitale Medien
    Digitale Medien
    MXAN : a new software procedure to perform geometrical fitting of experimental XANES spectra (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 267-269 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A new software procedure, MXAN, to fit experimental XANES spectra is presented here. The method is based on the comparison between the experimental spectrum and several theoretical calculations generated by changing the relevant geometrical parameter of the site around the absorbing atom. The x-ray photoabsorption cross section is calculated using the general multiple-scattering scheme, utilizing a complex Hedin-Lunqvist energy-dependent potential to describe the exchange correlation interaction. Our method has been applied to the study of geometrical environment of the tetrahedral zinc site of the protein superoxide dismutase (SOD). The experimental Zn K-edge XANES spectrum has been fitted in the space of the first shell coordination parameters (ligand distances and angles) following the behavior of the chi-square as a function of the local distortion from the starting crystallographic structure. The recovered structure is found to be independent on the starting conditions, showing the theoretical uniqueness of the structural solution. Strengths and limitations of the application to real systems are also discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049500015338
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  • 3
    Digitale Medien
    Digitale Medien
    Geometrical fitting of experimental XANES spectra by a full multiple-scattering procedure (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 1087-1094 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: In this paper a new software procedure is presented, named MXAN, able to fit the XANES part (from the edge to about 200 eV) of experimental X-ray absorption data. The method is based on the fitting between the experimental spectrum and several theoretical calculations generated by changing the relevant geometrical parameters of the site around the absorbing atom. The X-ray photoabsorption cross section is calculated using the full multiple-scattering scheme; different choices of the exchange correlation part of the potential can be utilized. To show the potentialities of the method the analysis of the nickel K-edge of the nickel ion in aqueous solution is presented. The procedure is able to recover the correct information on the symmetry and atomic distances from the experimental Ni K-edge XANES spectrum. The recovered structure is found to be independent of the starting conditions, showing the theoretical uniqueness of the structural solution.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049501006422
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  • 4
    Digitale Medien
    Digitale Medien
    NEXAFS multiple scattering calculations of KO2 (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 719-721 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Since many years the oxidation of alkali metals has being attracted much interest due to the catalytic properties of metal promoters and the simple electronic structure of alkali atoms. The alkali-oxides phase diagram indicates that the interaction of oxygen with alkali metals can lead to the formation of different atomic O2- ions and molecular O2- and O22- ions. Potassium superoxide has been prepared in situ and high resolution O k-edge absorption NEXAFS spectra have been measured at the VUV beam-line at ELETTRA facility. The experimental data have been analyzed by multiple scattering approach deriving many geometrical and electronic details. In particular, we have found that the growth material structure is of the KO2 type with an O-O distance of about 1.35Å and that the transition involving single π molecular empty state of the superoxide O2- anion has a fine structure. Multiple Scattering self consistent calculation indicates that the bond between oxygen anion and K atom is totally ionic and that the fine structure is essentially due to solid state effects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049501000206
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  • 5
    Digitale Medien
    Digitale Medien
    Double-channel excitation in the XAS spectra of divalent and trivalent iron complexes in water solution (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 213-214 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: We present a detailed analysis of XAS spectra of divalent and trivalent iron complexes in water solutions. The interpretation of the spectra has been provided by multi-channel multiple scattering approach. On this basis, good agreement between experimental data and theoretical calculations has been obtained in both cases including two excitation channels in the final state.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049500019282
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  • 6
    Digitale Medien
    Digitale Medien
    Multiple scattering approach to DAFS (2001)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 8 (2001), S. 396-397 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: In this article we outline a general approach to the anomalous correction to the atomic scattering factor ab initio calculation based on the multiple scattering theory. This approach can be used for structural determination in any system and in particular in the surfaces where symmetry conditions make usual analysis impossible. We show as an application of the formalism calculations related to experimental data of bulk Ge.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049500016526
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  • 7
    Digitale Medien
    Digitale Medien
    Local coordination geometry around Cu and Cu ions in silicate glasses: an X-ray absorption near edge structure investigation (2000)
    Springer
    The European physical journal 14 (2000), S. 211-216 
    Details
    ISSN: 1434-6036
    Schlagwort(e): PACS. 61.10.Ht X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. - 61.43.Fs Glasses - 85.40.Ry Impurity doping, diffusion and ion implantation technology
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: We present an X-ray absorption near edge structure (XANES) study on Cu+ and Cu2+ ions in silicate glasses at the Cu K-edge, aimed to determine the geometry of the local structure around the metal. This study is based on the comparison between experimental data and theoretical calculations made in the framework of multiple scattering theory. The XANES signals relative to several clusters are simulated on the basis of known crystalline structures involving Cu+ and Cu2+ ions in silicate matrices. Concerning the Cu2+ in glass, the simulations suggest the presence of a square coordination of oxygen atoms around the absorber, with a possible presence of metal ions in the second shell. As for the Cu+ ions, the metal clustering is excluded and a linear O-Cu-O coordination is evidenced.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100510050122
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