Double electron excitation in atomic Xe

An x-ray-absorption experiment on atomic Xe shows a clear evidence of the electron shakeup (off) from the ‘‘valence’’ shells when an L-shell electron is excited. A Δ self-consistent-field (ΔSCF) calculation in the dipole approximation was performed based on a local-exchange potential and the sudden approximation. The experimental results show that the model is qualitatively and semiquantitatively correct. Double electron excitations exhaust almost all of the multielectron oscillation strength, which is about 20% of the total. The lowest-lying shake-up channel was found in the calculation to contain more than 70% of the total double excitation strength, which is a significant overestimate compared to the experiment. The energy dependence of the overlap integral ${\mathit{S}}^2$ in the ΔSCF approximation is presented. Finally, an effect is noted that depends on the symmetry of the initial state being excited and is not explained by the ΔSCF theory. There is a difference between the ${\mathit{L}}_{\mathrm{I}}$ and ${\mathit{L}}_{\mathrm{II}}$,${\mathit{L}}_{\mathrm{III}}$ edges in the change in slope of the absorption curve in passing through the three identified two-electron excitations. This suggests that there is a quantum interference between the one- and two-electron excitations not accounted for by the theory.