Absolute cross sections for the transitions of the Kr atom into the 4s land 4p4nl states of the Kr + ion were measured in the 4s-electron threshold region by photon-induced fluorescence spectroscopy (PIFS). The cross sections for the transitions of the Kr atom into the 4sland 4p4nl states were also calculated, as weIl as the 4p4nln'I' doubly excited states, in the frame of LS-coupling many-body technique. The cross sections of the doubly-excited atomic states were used to illustrate the pronounced contributions of the latter to the photoionization process, evident from the measurements. The comparison of theory and experiment led to conclusions about the origin of the main features observed in the experiment.

Photon-induced fluorescence spectroscopy was applied for the first time to investigate the anisotropy of VUV radiation emitted from Kr II satellite states with total angular momentum J 3 2 after the photoionization of the Kr atom by linearly polarized synchrotron radiation near the 4s threshold. The measurements showed that the sign of the alignment parameter is practically independent of the exciting-photon energy for the ionic state with J = 5 2 , whereas for the states with J = 3 2 the alignment parameter changes sign with varying energy. Simple formulae connecting the angular distribution parameter and the alignment parameter with the kinematics of our experiment and with quantities describing the dynamics of the photoionization were derived in closed form. Partial and total cross sections for the photoionization of 4p, 4s and several satellite levels were calculated taking into account many-electron correlations and doubly-excited states. For the satellite states with J 3 2 the dependence of the angular distribution parameter on the exciting-photon energy was calculated. Good overall agreement between theory and experiment was obtained.

Absolute Kr 4s-eJectron photoionization cross sections as a function of the exciting-photon energy were measured by photon-induced fluorescence spectroscopy (PIFS) at improved primary-energy resolution. The cross sections were determined from threshold to 33.5 eV and to 90 eV with primary-photon bandwidths of 25 meV and 50 meV, respectively. The measurements were compared with experimental data and selected theoretical calculations for the direct Kr 4s-eJectron photoionization cross sections.

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The angular asymmetry parameter β fl of the photon-induced fluorescence radiation of Ar + (4p-4s) fine-structure resolved satellite lines was measured from threshold up to 38.4 eV. It is well known that the cross sections of these valence shell satellites are dominated by the decay of aligned doubly excited states leading to an extremely complicated energy dependence. In contrast, we observe that the β fl parameter becomes less structured with increasing total angular momentum J of the photoion. The β fl measurements can be interpreted by a partialwave analysis of the photofragmentation products. For the population of the 4p 2 F 7/2 ion state only d 5/2 photoelectrons are emitted on all resonances. For the population of the 4p 2 D 5/2 and the 4p 4 P 5/2 ion states the emission of the parity-unfavoured d 5/2 photoelectrons dominates.