Absolute photoionization cross sections along the Xe isonuclear sequence: Xe{sup 3+} to Xe{sup 6+}

Absolute photoionization cross sections of Xe{sup 3+} to Xe{sup 6+} ions have been measured over an extended photon energy range from the first ionization threshold to 160 eV. Single and double photoionization cross sections have been obtained. In the case of Xe{sup 3+} and Xe{sup 6+} ions, two completely independent setups, both based on the merged beam technique, have been used. Multiconfiguration Dirac-Fock calculations were performed to interpret the spectra in the region of 4d electron excitations. The partition of the oscillator strength between the discrete photoexcitation and the direct photoionization channels in the 4d subshell has allowed us to follow precisely the collapse of the 4f wave function for these ions of the isonuclear series of Xe.