MULTIELECTRON EXCITATIONS AT THE L EDGES OF BARIUM IN AQUEOUS-SOLUTION

An extensive investigation of the x-ray-absorption spectra above the L edges of a Ba2+ water solution is presented. Anomalous features are c learly detected in the spectra and have been associated with the creat ion of 2p4d and 2s4d double-core hole states for the L(3), L(2), and L (1) edges, respectively. A reliable determination of the double-electr on edge parameters has been obtained by performing a combined L-edge a nalysis in the correct framework of the radial distribution function t heory. Ba-O and Ba-H radial distribution functions have been calculate d by means of molecular-dynamics simulations and have been used as rel evant models in the calculation of the extended x-ray-absorption fine- structure (EXAFS) signals. The simultaneous analysis of the three edge s allowed an unambiguous characterization of the multielectron transit ion affecting the L, cross section. The experimental values of the ene rgy onsets of the double-electron features are in good agreement with previous theoretical calculations. The influence of multielectron tran sitions in the EXAFS data analysis is discussed. The neglect of double -electron excitation effects results in systematic errors on the struc tural parameters and in particular in an underestimation of the coordi nation numbers.