Using monochromatized extreme-UV radiation from the undulator beamline BW3 at HASYLAB we have measured at high resolution (E/ Delta E approximately 7000) the Li+ photoion yield spectrum at excitation energies corresponding to transitions to double K-shell vacancy states. A number of such resonances including single-photon-three-electron excitations, e.g. 1s22s(2S) to 2p3(2p), have been observed for the first time. The spectrum is tentatively classified with the aid of Hartree-Fock calculations.

The absolute photoabsorption cross section of atomic barium in the region of the 4d-giant resonance (80-140 eV) has been determined. The vapour density in the absorbing metal vapour column, required for the determination of the absolute cross sections was measured quasi-simultaneously with the absorption using a Mach-Zehnder interferometer. Our data show good agreement in terms of spectral signature with existing relative photoabsorption measurements. The measured absolute cross section corroborates the results of recent many-body calculations.