The L-level X-ray absorption spectra of atomic barium and mercury

The absorption spectra of L1, L2 and L3 levels of atomic Ba and Hg were measured. The spectra are interpreted in the one-electron picture using optical energies, in the Z+1 approximation for the final state. The absolute binding energies and L-level widths were determined. The binding energies are in good agreement with earlier solid-state measurements if the solid-state shift is taken into account. MCDF theory with full transverse Breit interaction predicts L2 and L3 level energies within experimental accuracy. L1 energies are too high by 2 and 5.7 eV for Ba and Hg respectively, which is due to QED corrections. The level widths of Hg L2 and L3 compare favourably with theory whereas all other levels are only half of the theoretical estimates. This discrepancy is attributed to wavefunctions calculated using local exchange and to the single-channel approximation in nonradiative rate calculations.