Geometrical structure of yttrium and metal-bromine complexes in solution: Limitations of extended X-ray absorption fine structure analysis (EXAFS)

An extensive study on the appearance of multi-electron features in the X-ra y absorption spectra of several yttrium(III)-based compounds has been perfo rmed. The existence of a multi-electron transition of non-negligible intens ity within the extended X-ray absorption fine structure (EXAFS) region of t he Y K-edge spectra has been proven. The impact of such features in the EXA FS analysis is made evident for aqueous solutions of YBr3 . 6H(2)O in liqui d and glassy states in the concentration range 0.005 -2.0M, in which this t ransition induces an overestimation in the coordination numbers derived fro m EXAFS. We have performed theoretical computation of cross-sections for th e double-electron processes at the K-edge of both Y and Br, These computati ons have been applied to the experimental EXAFS K-edge spectra of both Y an d Br in several solids and in aqueous solutions. While in the case of Y K-e dge spectra the presence of such multi-electron transitions was seen to ser iously affect the standard EXAFS analysis, its influence in the case of Br K-edge spectra was determined to be negligible.