K Edge (k + edge)

Distribution by Scientific Domains


Selected Abstracts


Application of the equivalent-core calculation to the Cl in core level on condensed SiCl4

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 13 2006
G. V. S. Mota
Abstract Utilization of the equivalent core may be of great help in the determination of excitation energies for condensed systems. This method presents a small difference in the excitation potential in relation to the experimental values, thus, enabling a better symmetry assignment for the excitations involved in the process. With the help of (Z+1)-core model, we estimated the absorption position and the symmetry for the discrete core-excitation state of the Cl K edge on SiCl4 and were able to understand the process of selective fragmentation for condensed systems with good calculation approximation. 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source]


Precursory microstructures in Zr,Cu,Al,Ni bulk metallic glasses examined by anomalous small-angle scattering at the Zr K edge

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2007
Isao Murase
Anomalous small-angle X-ray scattering measurements of Zr,Cu,Al,Ni quaternary alloys have been made at the Zr K absorption edge. In melt-quenched samples, small cluster components without crystallization were found. The contrast change at the edge suggested that compositional fluctuation of Al is incorporated. [source]


Symmetry role on the pre-edge X-ray absorption fine structure at the metal K edge

JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001
Ziyu Wu
The preedge features in a system with `even' symmetry, apart from quadrupolar transition contribution, are mainly dipolar in character, associated with the existence of unoccupied states made up of mixed cation-4p with higher-neighboring cation-3d orbitals, and reflect the density of states due to the medium-range order of the system. In `odd' symmetry materials these preedge features are the result of a transition from the 1s to a final density of states of p symmetry due to an unsymmetrical mixing of the ligand wave functions with the central cation 3d orbitals, similar to atetrahedral configuration. These results are validated for Fe as a photoabsorber by comparing XAS spectra of Fe2SiO4 (fayalite) to ab initio full multiple scattering calculations at the Fe K edge, but pertain to all systems containing sixfold-coordinated cations. [source]


Cover Picture: Plasma Process.

PLASMA PROCESSES AND POLYMERS, Issue 8 2005
Polym.
Cover: The Figure shows the X-ray photoelectron spectra of the nitrogen 1s core levels and the near edge X-ray fine structure nitrogen K edge of plasma polymers and plasma co-polymers prepared from allylamine and mixtures of acrylic acid and allylamine. Molecular models of allylamine, acrylic acid and allylammonium acrylate salt are shown to illustrate the chemistry. This is shown on a background of a micrograph of melanocytes cultured on a plasma polymer coating. The micrograph has been artificially colourised. Further details can be found in the Full Paper by A. J. Beck,* J. D. Whittle, N. A. Bullett, P. Eves, S. Mac Neil, S. L. McArthur, and A. G. Shard on page 641. [source]


Determination of zinc incorporation in the Zn-substituted gallophosphate ZnULM-5 by multiple wavelength anomalous dispersion techniques

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010
M. Helliwell
The location of isomorphously substituted zinc over eight crystallographically different gallium sites has been determined in a single-crystal study of the gallophosphate ZnULM-5, GaZn(PO4)14(HPO4)2(OH)2F7, [H3N{CH2}6NH3]4, 6H2O, in an 11 wavelength experiment, using data from Station 9.8, SRS Daresbury. The measurement of datasets around the K edges of both Ga and Zn, as well as two reference datasets away from each absorption edge, was utilized to selectively exploit dispersive differences of each metal atom type in turn, which allowed the major sites of Zn incorporation to be identified as the metal 1 and 3 sites, M1 and M3. The preferential substitution of Zn at these sites probably arises because they are located in double four-ring (D4R) building units which can relax to accommodate the incorporation of hetero atoms. As the crystal is non-centrosymmetric, with space group P21212, it was also possible to use anomalous differences to corroborate the results obtained from the dispersive differences. These results were obtained firstly from difference Fourier maps, calculated using a phase set from the refined structure from data measured at the Zr K edge. Also, refined dispersive and anomalous occupancies, on an absolute scale, could be obtained using the program MLPHARE, allowing estimates for the Zn incorporation of approximately 22 and 18 at. % at the M1 and M3 sites to be obtained. In addition, f, and f,, values for Ga and Zn at each wavelength could be estimated both from MLPHARE results, and by refinement in JANA2006. The fully quantitative determinations of the dispersive and anomalous coefficients for Ga and Zn at each wavelength, as well as metal atom occupancies over the eight metal atom sites made use of the CCP4's MLPHARE program as well as SHELXL and JANA2006. The results by these methods agree closely, and JANA2006 allowed the ready determination of standard uncertainties on the occupancy parameters, which were for M1 and M3, 20.6,(3) and 17.2,(3),at %, respectively. [source]


THE SECTILIA PANELS OF FARAGOLA (ASCOLI SATRIANO, SOUTHERN ITALY): A MULTI-ANALYTICAL STUDY OF THE GREEN, MARBLED (GREEN AND YELLOW), BLUE AND BLACKISH GLASS SLABS

ARCHAEOMETRY, Issue 3 2010
E. GLIOZZO
Analyses at the Cu,K, Fe,K and Mn,K edge were performed to study the green, marbled (green and yellow), blue and blackish (deep greyish olive green) glass slabs decorating three sectilia panels from the archaeological site of Faragola. Results indicate that all slabs were made by mixing siliceous sand with natron, sometimes probably mixed with small percentages of plant ash. Cu2+ and Pb antimonates should be responsible for the opaque green colours. The dark green and yellow portions of the marbled slabs are respectively comparable to the slabs comprising only one of these colours. Cu2+ together with Ca antimonates probably produced light blue slabs, whereas cobalt was used to produce dark blue slabs. We consider it possible that the abundance ratio of Fe2+/Fe3+ and the complex Fe3+S2, would have an effect on the blackish slabs. The contribution of Mn cannot be ascertained even if it could have played a role in darkening glass colour. The comparison between the chemical composition of Faragola samples and several glass reference groups provided no conclusive evidence of provenance; whereas, the presence of a secondary local workshop can be hypothesized. [source]


The magic triangle goes MAD: experimental phasing with a bromine derivative

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2010
Tobias Beck
Experimental phasing is an essential technique for the solution of macromolecular structures. Since many heavy-atom ion soaks suffer from nonspecific binding, a novel class of compounds has been developed that combines heavy atoms with functional groups for binding to proteins. The phasing tool 5-amino-2,4,6-tribromoisophthalic acid (B3C) contains three functional groups (two carboxylate groups and one amino group) that interact with proteins via hydrogen bonds. Three Br atoms suitable for anomalous dispersion phasing are arranged in an equilateral triangle and are thus readily identified in the heavy-atom substructure. B3C was incorporated into proteinase K and a multiwavelength anomalous dispersion (MAD) experiment at the Br,K edge was successfully carried out. Radiation damage to the bromine,carbon bond was investigated. A comparison with the phasing tool I3C that contains three I atoms for single-wavelength anomalous dispersion (SAD) phasing was also carried out. [source]


Narrow-Line Seyfert 1 Galaxies with high-energy sharp spectral drops: reflection-versus absorption models

ASTRONOMISCHE NACHRICHTEN, Issue 10 2006
Th. Boller
Abstract With the launch of XMM-Newton in 1999, two Narrow-Line Seyfert 1 Galaxies (NLS1s) have been detected (IRAS 13224,3809 and 1H 0707,495) showing sharp spectral drops at energies equal or above the neutral Fe K edge at 7.1 keV without any narrow Fe K reemission. In this paper I summarize our present knowledge on the observed properties of sharp high-energy spectral drops. I list the problems presently arising from the reflection dominated and the optically thick disc models. Finally, I present an alternative solution which consists of a combination of the accretion disc model and the reflection dominated model. This might solve the problems of the standard accretion disc model. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Phasing power at the K absorption edge of organic arsenic

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2003
Pascal Retailleau
Single/multiple-wavelength anomalous dispersion (SAD/MAD) experiments were performed on a crystal of an organic arsenic derivative of hen egg-white lysozyme. A para -arsanilate compound used as a crystallizing reagent was incorporated into the ordered solvent region of the lysozyme molecule. Diffraction data were collected to high resolution (,2.0,) at three wavelengths around the K edge (1.04,) of arsenic at beamline BM30A, ESRF synchrotron. Anomalous Patterson maps clearly showed the main arsanilate site to be between three symmetry-related lysozyme molecules, at a location previously occupied by a para -toluenesulfonate anion. MAD phases at 2, derived using the program SHARP led to an electron-density map of sufficient quality to start manual building of the protein model. Amplitudes from a second crystal measured to a resolution of 1.8, at the peak wavelength revealed two additional heavy-atom sites, which reinforced the anomalous subset model and therefore dramatically improved the phasing power of the arsenic derivative. The subsequent solvent-flattened map was of such high accuracy that the program ARP/wARP was able to build a nearly complete model automatically. This work emphasizes the great potential of arsenic for de novo structure determination using anomalous dispersion methods. [source]


Calculation of XANES/ELNES Spectra of All Edges in Si3N4 and Si2N2O

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002
Wai-Yim Ching
Using a recently developed first-principles supercell method that includes the electron and core-hole interaction, the XANES/ELNES spectra of Si- L2,3, Si- K, and N- K edges in ,-Si3N4, ,-Si3N4, spinel c -Si3N4, and Si2N2O were calculated and compared. The difference in total energies between the initial ground state and the final core-hole state provides the transition energy. The calculated spectra are found to be in good agreement with the experimental measurements on ,-Si3N4 and c -Si3N4. The differences in the XANES/ELNES spectra for the same element in different crystals are explained in terms of differences in local bonding. The use of orbital-decomposed local density of states to explain the measured spectra is shown to be inadequate. These results reaffirm the importance of including the core-hole effect in any XANES/ELNES spectral calculation. [source]


Determination of zinc incorporation in the Zn-substituted gallophosphate ZnULM-5 by multiple wavelength anomalous dispersion techniques

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2010
M. Helliwell
The location of isomorphously substituted zinc over eight crystallographically different gallium sites has been determined in a single-crystal study of the gallophosphate ZnULM-5, GaZn(PO4)14(HPO4)2(OH)2F7, [H3N{CH2}6NH3]4, 6H2O, in an 11 wavelength experiment, using data from Station 9.8, SRS Daresbury. The measurement of datasets around the K edges of both Ga and Zn, as well as two reference datasets away from each absorption edge, was utilized to selectively exploit dispersive differences of each metal atom type in turn, which allowed the major sites of Zn incorporation to be identified as the metal 1 and 3 sites, M1 and M3. The preferential substitution of Zn at these sites probably arises because they are located in double four-ring (D4R) building units which can relax to accommodate the incorporation of hetero atoms. As the crystal is non-centrosymmetric, with space group P21212, it was also possible to use anomalous differences to corroborate the results obtained from the dispersive differences. These results were obtained firstly from difference Fourier maps, calculated using a phase set from the refined structure from data measured at the Zr K edge. Also, refined dispersive and anomalous occupancies, on an absolute scale, could be obtained using the program MLPHARE, allowing estimates for the Zn incorporation of approximately 22 and 18 at. % at the M1 and M3 sites to be obtained. In addition, f, and f,, values for Ga and Zn at each wavelength could be estimated both from MLPHARE results, and by refinement in JANA2006. The fully quantitative determinations of the dispersive and anomalous coefficients for Ga and Zn at each wavelength, as well as metal atom occupancies over the eight metal atom sites made use of the CCP4's MLPHARE program as well as SHELXL and JANA2006. The results by these methods agree closely, and JANA2006 allowed the ready determination of standard uncertainties on the occupancy parameters, which were for M1 and M3, 20.6,(3) and 17.2,(3),at %, respectively. [source]