Evidence for double-electron excitations in theL3-edge x-ray absorption spectra of actinides

A double-electron excitation in $L_3$-edge x-ray absorption spectra of actinides has been observed for the first time. The investigation of this effect is presented. Actinide species in valence states IV and III were investigated by using experimental data of ${\mathrm{Th}}^{4+}$, ${\mathrm{U}}^{4+}$, ${\mathrm{Np}}^{4+}$, ${\mathrm{Pu}}^{3+}$, and ${\mathrm{Am}}^{3+}$ hydrates. The double-electron excitation was identified as a $L_3{N}_{6,7}$ shake-up effect. Energy positions of the double-electron features were found in good agreement with the $Z+1$ approximation. The $LN$ resonance intensity corresponds with the resonance of the $L$ edge. This has been observed by comparing the $L_1$, $L_2$, and $L_3$ XANES spectra of ${\mathrm{Th}}^{4+}$, as well as the $L_3$ XANES spectra of Np in oxidation states IV, V, VI, and VII. Influences of the double-electron excitation on the EXAFS signal are discussed.