scholarly journals Pinpointing and Quantifying the Aluminum Distribution in Zeolite Catalysts Using Anomalous Scattering at the Al Absorption Edge

2021 ◽  
Author(s):  
Ana B. Pinar ◽  
Przemyslaw Rzepka ◽  
Amy J. Knorpp ◽  
Lynne B. McCusker ◽  
Christian Baerlocher ◽  
...  
Keyword(s):  
Absorption Edge ◽  
Zeolite Catalysts ◽  
Anomalous Scattering ◽  
Aluminum Distribution

CHOOCH: a program for deriving anomalous-scattering factors from X-ray fluorescence spectra

2001 ◽  
Vol 34 (1) ◽  
pp. 82-86 ◽  
Author(s):  
Gwyndaf Evans ◽  
Robert F. Pettifer
Keyword(s):  
Absorption Edge ◽  
Fluorescence Spectra ◽  
Heavy Atom ◽  
Fortran Program ◽  
Anomalous Scattering ◽  
Tabular Data ◽  
X Ray ◽  
Scattering Factor ◽  
Experimental Values ◽  
Kronig Relation

A Fortran programCHOOCH, which derives experimental values of the anomalous-scattering factorsf′′ andf′ from X-ray fluorescence spectra, is described. The program assumes knowledge of theoretical values for the imaginary term,f′′, of the anomalous-scattering factor away from the absorption edge to scale the experimental fluorescence spectrum and thus derive values off′′ near the absorption edge, where tabular data are inappropriate. The Kramers–Kronig relation is used to calculate the real part,f′, of the anomalous-scattering factor. The program aids the decision-making process in macromolecular crystallographic experiments where optimal wavelength selection is required. Magnitudes off′ andf′′ at selected wavelengths can later be used as starting values for heavy-atom refinement with crystallographic phasing programs.

The information available from anomalous scattering on fibres at different wavelengths

1987 ◽  
Vol 20 (4) ◽  
pp. 295-299 ◽  
Author(s):  
C. Nave
Keyword(s):  
Absorption Edge ◽  
Heavy Atom ◽  
Imaginary Component ◽  
Anomalous Scattering ◽  
Phase Problem ◽  
Phase Information ◽  
Helical Symmetry ◽  
X Ray ◽  
The Real ◽  
X Ray Scattering

The contribution of a particular atom in a molecule to the total X-ray scattering can be altered by varying the wavelength in the region of the absorption edge of the atom. It is shown that only the changes in the real part of the anomalous scattering of the atom provide significant changes in a pattern from a fibre containing molecules with helical symmetry. Changes due to the imaginary component are small and Friedel differences cannot be observed, owing to the fibre disorder. The information which can be obtained is equivalent to that given by a truly isomorphous heavy-atom derivative. For the general case this is not sufficient to provide unambiguous phase information. If a twofold axis is present at right angles to the fibre axis then the amplitudes are real and the phase problem can, in favourable cases, be solved.

A Rietveld-analysis program for X-ray powder spectro-diffractometry

1999 ◽  
Vol 14 (2) ◽  
pp. 106-110 ◽  
Author(s):  
Yanan Xiao ◽  
Shinjiro Hayakawa ◽  
Yohichi Gohshi ◽  
Masaharu Oshima ◽  
Fujio Izumi ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Powder Diffraction ◽  
Absorption Edge ◽  
Rietveld Method ◽  
Rietveld Analysis ◽  
Anomalous Scattering ◽  
Analysis Program ◽  
X Ray ◽  
Diffraction Patterns ◽  
X Ray Absorption

In order to exploit X-ray powder spectro-diffractometry, the program RIETAN-97ß for refining crystal structure and lattice parameters by the Rietveld method was modified extensively. The resulting software can be used to refine anomalous scattering factors, fr and fi, for specified crystallographic sites near the X-ray absorption edge of a particular element. The effectiveness of the modified software was tested by using powder diffraction patterns simulated by the original RIETAN-97ß software and a series of measured powder diffraction patterns of Fe3O4 with incident X-ray energies near the absorption edge of iron.

Determination of Anomalous Scattering Factor by Using Transmitted Rocking Curves near the Absorption Edge

1997 ◽  
Vol 36 (Part 1, No. 10) ◽  
pp. 6424-6425 ◽  
Author(s):  
Shengming Zhou ◽  
Masami Yoshizawa ◽  
Tomoe Fukamachi ◽  
Riichiro Negishi ◽  
Takaaki Kawamura ◽  
...  
Keyword(s):  
Absorption Edge ◽  
Anomalous Scattering ◽  
Scattering Factor

X-ray determination of polarity sense by anomalous scattering at an absorption edge

1970 ◽  
Vol 3 (1) ◽  
pp. 27-32 ◽  
Author(s):  
R. L. Barns ◽  
E. T. Keve ◽  
S. C. Abrahams
Keyword(s):  
Absorption Edge ◽  
Anomalous Scattering ◽  
X Ray

scholarly journals Crystallographic studies on Mn atoms in Photosystem II using K-edge wavelength

2014 ◽  
Vol 70 (a1) ◽  
pp. C350-C350
Author(s):  
Yasufumi Umena ◽  
Keisuke Kawakami ◽  
Jian-Ren Shen ◽  
Nobuo Kamiya
Keyword(s):  
Photosystem Ii ◽  
Molecular Oxygen ◽  
Electronic State ◽  
Absorption Edge ◽  
Water Oxidation ◽  
Catalytic Mechanism ◽  
Anomalous Scattering ◽  
Oxygen Evolving Complex ◽  
X Ray ◽  
Difference Fourier

Molecular oxygen on Earth is generated from photosynthesis by cyanobacteria, algae and plants, where water molecules are split by Photosystem II (PSII). PSII catalyzes light-induced water oxidation leading to the production of protons, electrons and molecular oxygen. The catalytic center of oxygen evolving complex (OEC) in PSII is composed of four Mn atoms and one Ca atom organized in a Mn4CaO5-cluster, which cycles through several different redox states to accomplish the catalytic process. Cyanobacterial PSII is a multi-subunits membrane protein complex composed of 17 membrane-spanning subunits, 3 membrane-extrinsic subunits and about 80 co-factor molecules with a total molecular weight of 350 kDa as a monomer. We reported the PSII structure at 1.9 Å resolution prepared from Thermosynechococcus vulcanus (PDB code: 3ARC)[1]. We determined unambiguously the positions of the atoms in OEC using the electron density map corresponding to each of five metal atoms and five oxygen atoms, for the first time. However, the valences of each of the four Mn atoms and their participation in the redox reactions in OEC are not fully understood. In order to uncover the catalytic mechanism of light-induced water oxidation by OEC, it is important to determine the valence of each Mn atom as well as to solve the detailed structure. In this study, we analyze the electronic state of each Mn atom in OEC by X-ray crystallographic analysis using Mn K-absorption edge wavelength. The Mn K-absorption edge depends on the oxidation number, and the anomalous scattering factor changes greatly for the Mn atoms in different oxidation states. We collected the anomalous difference data from PSII crystals using the wavelength (~1.8921 Å) on the Mn K-absorption edge at beamline BL38B1 and BL41XU of SPring-8 in Japan. The calculated anomalous difference Fourier map indicated different intensities among the four Mn atoms in OEC. This may suggest the different electronic state among the four Mn atoms in OEC. However, there is a possibility that these Mn atoms are reduced by X-ray exposures to some extent, and so the valences of these Mn atoms were not determined completely. We will discuss the relationship between peak heights of the anomalous difference Fourier map and the valence among the four Mn atoms in OEC.

Measurements of X-Ray Anomalous Scattering Factors near the Cu K Absorption Edge by the Use of Synchrotron Radiation

1978 ◽  
Vol 17 (S2) ◽  
pp. 326 ◽  
Author(s):  
Tomoe Fukamachi ◽  
Sukeaki Hosoya ◽  
Takaaki Kawamura ◽  
Sally Hunter ◽  
Yuji Nakano
Keyword(s):  
Synchrotron Radiation ◽  
Absorption Edge ◽  
Anomalous Scattering ◽  
X Ray

Valence-difference contrast measurements utilizing X-ray anomalous scattering

1998 ◽  
Vol 5 (3) ◽  
pp. 920-922 ◽  
Author(s):  
Satoshi Sasaki ◽  
Takeshi Toyoda ◽  
Kouji Yamawaki ◽  
Koichi Ohkubo
Keyword(s):  
Absorption Edge ◽  
Low Temperatures ◽  
Diffuse Scattering ◽  
Charge Ordering ◽  
Anomalous Scattering ◽  
Valence Fluctuation ◽  
X Ray ◽  
Contrast Method ◽  
Valence States ◽  
Scattering Measurements

Anomalous scattering experiments with X-ray wavelengths close to an absorption edge have made it possible to determine independently the behaviour of ions in different valence states. The anomalous scattering factors of Fe2+ and Fe3+ obtained from both absorption and diffraction data have a large difference in f′ between the two kinds of ions. Using a valence-difference contrast method, Bragg and diffuse scattering measurements were carried out for single crystals of Fe3O4 at low temperatures. The results demonstrate the ability of the contrast method to resolve charge ordering and valence fluctuation details.

Anomalous grazing-incidence small-angle X-ray scattering of Ga2O3-based nanoparticles

2018 ◽  
Vol 51 (2) ◽  
pp. 436-445 ◽  
Author(s):  
Christine Revenant
Keyword(s):  
Absorption Edge ◽  
Small Angle ◽  
Incident Angle ◽  
Grazing Incidence ◽  
Core Shell ◽  
Dense Layer ◽  
Anomalous Scattering ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

Grazing-incidence small-angle X-ray scattering (GISAXS) performed at several X-ray energies in the vicinity of the absorption edge of a considered element is called anomalous GISAXS (AGISAXS). This emerging technique takes advantage of the variation of the scattering factor near an absorption edge, allowing the morphology of multi-component nanomaterials to be unraveled. The selected model system for AGISAXS simulations is mainly an In2O3layer containing Ga2O3-based nanoparticles. The transmission coefficients at the different X-ray energies near the GaKedge are identical at one specific incident angle (near the critical angle). Hence, it could be relevant to perform AGISAXS at this incident angle in order to cancel the transmission modification as the X-ray energy changes. For buried nanoparticles, grazing-incidence effects are negligible with respect to the anomalous element-specific contribution provided that the experiments are performed at energies a few electronvolts below the absorption edge. Interestingly, AGISAXS has a clearly different intensity behaviorversusX-ray energy for an embedded monodisperse spherical particle, a hole and a core–shell particle. Hence, AGISAXS can be used to unambiguously distinguish such embedded particles. Moreover, even for a dense layer of core–shell nanoparticles on a substrate, anomalous effects are much larger than grazing effects as the X-ray energy changes. Finally, it is shown that experimental anomalous scattering can be significant and can be satisfactorily simulated.

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