4d Photoionization of multiply charged Xe^q+ (q = 1-3) ions

Using a photon-ion merged-beam technique, we studied the photoionization of multiply charged Xeq+ (q = 1-3) ions in the 4d excitation region (50-140eV). Relative yield spectra of photoions created by single (q-->q+1) and double (q-->q+2) photoionization were measured as a function of photon energy. A broad "4d giant resonance" peak with some preceding discrete peaks appears in each total ion spectrum. The intensities of discrete peaks observed at around 4d ionization threshold strongly depend on the target charge state. Those for Xe3+ target are very strong, whereas those for Xe+ are weak. Peaks due to 4d-->5p transition, which cannot occur in the neutral Xe case, has also been observed for each ion-target. The experimental spectrum for Xe+ has been analyzed by a multiconfiguration Dirac-Fock calculation This calculation shows that results observed may be explained in terms of the correlation of valence and excited orbitals, and the effect of 4f-orbital collapse, of which the degree varies strongly with the change of the effective nuclear charge.