EVIDENCE FOR MULTIELECTRON RESONANCES AT THE SR K-EDGE

X-ray-absorption spectra of a Sr2+ aqueous solution have been studied in order to assess the contribution of double-electron excitation chan nels to the atomic background. Anomalies in the spectra have been iden tified that are assigned to the simultaneous excitation of 1s4s, 1s3d, and 1s3p electrons, referred to as KN1, KM(4,5) and KM(2,3) channels. A reliable determination of the double-electron edge parameters has b een obtained by performing an analysis of the structural contribution in the correct framework of the radial distribution function theory. T he experimental values of the energy onsets of the double-electron fea tures are in excellent agreement with the predictions of the Z+1 appro ximation. The influence of double-electron effects on the determinatio n of the structural parameters has been studied by using asymmetric pe aks to model the Sr-O and Sr-H coordination shells. It has been found that an accurate determination of the structural parameters is possibl e only if double-electron channels are accounted for. The exclusion of these effects results in systematic errors on the structural paramete rs and, in particular, in a severe underestimation of the coordination numbers.