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 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 KN1, 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 Z+1 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.