Evidence for multielectron resonances at the SrKedge

Abstract

X-ray-absorption spectra of a Sr 2ϩ aqueous solution have been studied in order to assess the contribution of double-electron excitation channels to the atomic background. Anomalies in the spectra have been identified that are assigned to the simultaneous excitation of 1s4s, 1s3d, and 1s3p electrons, referred to as KN 1 , KM 4,5 , and KM 2,3 channels. A reliable determination of the double-electron edge parameters has been obtained by performing an analysis of the structural contribution in the correct framework of the radial distribution function theory. The experimental values of the energy onsets of the double-electron features are in excellent agreement with the predictions of the Zϩ1 approximation. The influence of double-electron effects on the determination of the structural parameters has been studied by using asymmetric peaks to model the Sr-O and Sr-H coordination shells. It has been found that an accurate determination of the structural parameters is possible only if double-electron channels are accounted for. The exclusion of these effects results in systematic errors on the structural parameters and, in particular, in a severe underestimation of the coordination numbers.

Structural Investigation of the Aqueous Eu2+ Ion: Comparison with Sr2+ Using the XAFS Technique

“…In recent years, several studies on Sr 2+ in aqueous solution using XAFS, [15][16][17][18][19][20][21] neutron 22 and X-ray 23 diffraction, and molecular dynamics simulation 24,17,21 have been performed. Unfortunately they showed widespread results concerning Sr-O distances as well as coordination numbers (from 7 to 10).…”

Determination of two- and three-body correlation functions in ionic solutions by means of MD and EXAFS investigations

“…4. Note that the presence of double-electron excitations in the Sr absorption background has been accounted for in the extraction of the x(k) experimental spectrum (D'Angelo et al, 1996b). The agreement between the theoretical and the experimental signals is not satisfactory, especially in the low-k region of the spectrum.…”

“…A method which uses MD radial distribution functions as relevant models in the calculation of the EXAFS structural signal of disordered systems has been employed to study the solvation shells of several ions in solution (D'Angelo et al, 1994, 1996a, 1996b, 1996c, Roccatano et al, 1998.…”

“…Alkaline and alkaline earth ions give rise to a non-regular coordination in aqueous and non-aqueous solutions (D'Angelo et al,1996b, 1996c, Roccatano et al, 1998. Nevertheless, in some cases the presence of three-body correlation functions can still be detected.…”

“…The local structure of ions dissolved in aqueous and non-aqueous solutions has been extensively studied by means of x-ray absorption spectroscopy (D'Angelo et al, 1996a, 1996b, 1996c, 1997, Roccatano et al, 1998. This technique offers the unique opportunity to probe the local coordination of ions in solution.…”