Evidence for double-electron excitations in X-ray absorption spectra of actinides

A systematic investigation of double-electron resonances in L3 edge X-ray absorption spectra of actinides in aqueous solution is presented. Actinide species in valence states IV and III were investigated by using experimental data of Th4+, U4+, Np4+, Pu3+, and Am3+ hydrates. The double-electron excitation was identified as a L3N6,7 shake-up effect. Energy positions of the double-electron features were found in good agreement with the Z+1 approximation. The double-electron resonances undergo a larger chemical shift as the L3 edge.