Geometrical Structure of Yttrium and Metal-Bromine Complexes in Solution: Limitations of Extended X-ray Absorption Fine Structure Analysis (EXAFS)

Abstract

An extensive study on the appearance of multi-electron features in the X-ray absorption spectra of several yttrium(III)-based compounds has been performed. The existence of a multi-electron transition of non-negligible intensity within the extended X-ray absorption fine structure (EXAFS) region of the Y K-edge spectra has been proven. The impact of such features in the EXAFS analysis is made evident for aqueous solutions of YBr3 x 6H2O in liquid and glassy states in the concentration range 0.005-2.0 M, in which this transition induces an overestimation in the coordination numbers derived from EXAFS. We have performed theoretical computation of cross-sections for the double-electron processes at the K-edge of both Y and Br. These computations have been applied to the experimental EXAFS K-edge spectra of both Y and Br in several solids and in aqueous solutions. While in the case of Y K-edge spectra the presence of such multi-electron transitions was seen to seriously affect the standard EXAFS analysis, its influence in the case of Br K-edge spectra was determined to be negligible.

Ab initio X-ray Absorption Spectroscopy Study of the Solvation Structure of Yttrium (III) in Dimethyl Sulfoxide

“…To this end, the XANES spectrum of the 0.5 M solution of YSCN in acetonitrile has been computed from ab initio methods. Finally, and before addressing the determination of the solvation structure of the Y(III) in DMSO solution, we have performed the computation of the XANES in its parent solid compound YDMSO, 29 the structure of which has been fully determined by XRD. 30 In the case of the YNCS acetonitrile solution the computation was performed using a cluster of 19 atoms around the absorbing atom.…”

Local Structure Refinement of Disordered Material Models: Ion Pairing and Structure in YCl3Aqueous Solutions

“…On comparison with the experimental data model 2 results in an estimation of the EXAFS signal from the Y 3+ ion that is comparable in quality with a conventional direct analysis . The spectral feature at ≈7.2 Å -1 arises from the simultaneous excitation of an Y 3+ 3d electron to a 4d level with the principle X-ray excitation of the Y 3+ 1s electron to a 5p level . As multielectron excitations are not included in the basic FEFF calculation of the EXAFS signal, this feature is absent from the model.…”

“…4 The spectral feature at ≈7.2 Å -1 arises from the simultaneous excitation of an Y 3+ 3d electron to a 4d level with the principle X-ray excitation of the Y 3+ 1s electron to a 5p level. 28 As multielectron excitations are not included in the basic FEFF calculation of the EXAFS signal, this feature is absent from the model. Figure 5 demonstrates the sensitivity of the X-ray absorption data to the details of the local atomic interaction potentials through a comparison of the Y 3+ -O water potential that results from the two choices of Lennard-Jones σ.…”