XANES

About: XANES is a research topic. Over the lifetime, 7737 publications have been published within this topic receiving 188032 citations.

The CO bond angle of carboxymyoglobin determined by angular-resolved XANES spectroscopy.

Abstract: Our knowledge of the structure of condensed matter has been based primarily on spectroscopic methods that measure first-order pair correlations of atomic arrangements and thus provide interatomic distances (for example neutron and X-ray scattering). Bond angles are given by higher-order correlation functions, and such information can be provided by X-ray absorption near-edge structure (XANES) spectroscopy, the features of which are determined by multiple scattering of photoelectrons whose paths begin and end at the selected absorbing atom. We report here angular-resolved XANES spectroscopy of a single crystal of carboxymyoglobin (MbCO). The large dichroism of the X-ray absorption of the crystal can be fully interpreted by multiple-scattering theory which allows the determination of Fe-ligand bond angles. The analysis of the identified multiple scattering features due to CO in high signal-to-noise-ratio spectra of protein in solution has allowed the determination of the variation of CO bond angles. This opens the way to the determination of subtle structural features due to bond angle variations in proteins in solution which are relevant to an understanding of the characteristics of proteins at the atomic scale.

Multiple-scattering calculations of the uranium L 3 -edge x-ray-absorption near-edge structure

Abstract: A theoretical study of the uranium ${\mathit{L}}_{3}$-edge x-ray absorption near-edge structure (XANES) is presented for several uranium compounds, including oxides, intermetallics, uranyl fluoride, and \ensuremath{\alpha}-uranium Calculations were performed using feff6, an ab initio multiple-scattering (MS) code that includes the most important features of current theories The results, which account for both the fine structure \ensuremath{\chi} and the atomiclike background ${\mathrm{\ensuremath{\mu}}}_{0}$ of the absorption coefficient \ensuremath{\mu}, are compared to new and previously measured experimental spectra, reavealing very good agreement for most systems For several compounds, a more detailed theoretical analysis determined the influence of cluster size and scattering order upon the calculated spectra Results indicate that MS paths and scattering paths that include rather distant atoms make significant contributions for ${\mathrm{UO}}_{2}$, whereas XANES for crystals with lower symmetry and density can be modeled using only shorter single-scattering paths In most cases, assumption of a screened final state in the calculation gives better agreement with experiment than use of an unscreened final state The successful modeling of spectra for a variety of different uranium compounds, with differing spectral features, indicates that the semirelativistic treatment of XANES used here is adequate even for heavy elements The well-known resonance, observed experimentally for uranyl (${\mathrm{UO}}_{2}^{2+}$) compounds \ensuremath{\approxeq}15 eV above the white line, is successfully modeled here for the first time, using multiple-scattering paths within the O-U-O axial bonds Overlapping muffin-tin spheres were required in the calculation, probably as a result of the short uranyl axial bonds

MXAN: a new software procedure to perform geometrical fitting of experimental XANES spectra.

Abstract: 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.

Enhanced Thermal Stability and Oxygen Storage Capacity for CexZr1-xO2 (x = 0.4−0.6) Solid Solutions by Hydrothermally Homogenous Doping of Trivalent Rare Earths

Abstract: Trivalent rare-earth (RE = La, Pr, Nd, Y)-doped CexZr1-xO2 (x = 0.4−0.6) solid solutions were synthesized via a urea hydrolysis-based hydrothermal method, followed by calcination at 1000 °C for 100 h. The X-ray absorption near-edge structure (XANES) tests for the Ce LIII edge determine that the chemical valence of the Ce atom in either undoped or RE-doped CeO2−ZrO2 samples was mainly +4. The measurements of X-ray fluorescence (XRF) and energy-filtered transmission electron microscopy (EFTEM) testify to the good compositional homogeneity for Ce, Zr, and RE atoms in both bulk and microdomain of the as-calcined CexZr1-x-yREyO2-z (x = 0.4−0.6, y = 0−0.16, and z is the number of oxygen vacancy) samples. The characterizations with X-ray diffraction (XRD) and vis-Raman demonstrate the high structural homogeneity for ternary CeO2−ZrO2−RE2O3 solid solutions after calcination at 1000 °C for 100 h. The aliovalent substitution of the RE3+ ion for the Ce4+ or Zr4+ ion has been concluded to stabilize the pseudo cubic t...

In situ x-ray absorption spectroscopic study of the Li[Ni1∕3Co1∕3Mn1∕3]O2 cathode material

Abstract: The layered LiNi1∕3Co1∕3Mn1∕3O2 system has recently drawn considerable interest for use as a cathode material for rechargeable lithium batteries. In order to investigate the charge-compensation mechanism and structural perturbations occurring in the system during cycling, in situ x-ray absorption spectroscopy (XAS) measurements were performed utilizing a novel electrochemical in situ cell specifically designed for long term x-ray experiments. The cell was cycled at a moderate rate through a typical Li-ion battery operating voltage range (2.9–4.7 V). The electrode contained 2.025 mg of LiNi1∕3Co1∕3Mn1∕3O2 on a 25-μm Al foil and had an area of 0.79cm2. The x-ray absorption spectroscopy (XAS) measurements were performed at the Ni, Co, and the Mn edges at different states of charge (SOC) during cycling, revealing details about the response of the cathode to Li insertion and extraction processes. Changes of bond distance and coordination number of Ni, Co, and Mn absorbers as a function of the state of charge o...