Partial cross sections and angular-distribution asymmetry parameters were measured for subshell photoionization of xenon for photon energies between 40 and 1000 eV. These large-scale measurements show that the pronounced interchannel coupling between the valence and the 4d electrons persists beyond the 4d shape resonance in the subsequent Cooper-minimum region. Multielectron processes associated with 4d and 4p photoemission were measured directly for the first time over a broader energy range covering the near-threshold behavior up to the sudden limit. Comparing our experimental results with calculations based on the single-particle model shows that this theory, which fails to describe the intermediate energy range even qualitatively for the valence electrons, gives partial cross sections in reasonable agreement with experiment at higher photon energies, particularly beyond the 3d threshold. The same result is shown by the angular-distribution asymmetry parameter P, except for the photoionization of the "4p" subshell which resembles more the behavior of a 4d electron, corroborating the theoretical assumptions of core-hole fluctuations between these two subshells. In the shape resonance region the presented 4d partial cross sections are in reasonable agreement with theoretical results obtained recently by many-body perturbation theory.

A theoretical and experimental study of the behaviour of the correlation satellites arising during 5s photoionization of xenon is presented. Many-body perturbation theory and configuration-interaction techniques have been applied to calculate the wavefunctions of the Xe II ionic states. An expression for the angular distribution parameter of the photoelectrons taking into account final-ionic-state configuration interaction is derived. Photoionization cross sections and angular distribution parameters were calculated for the 5s main line and the majority of the satellite lines and compared with our high-resolution measurements and earlier lower resolution measurements.The differences in the angular distribution parameter dependence on the photon energy for the 5s main line and satellites were analysed in terms of their origin. The most important mechanisms are: interference of several photoionization channels characterizing different orbital momenta of the photoelectron, the mixture of terms with different total orbital momenta in the final ionic state, and the dependence of the photoelectron wavefunctions on the total momentum of the photoelectrons.

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The independent particle approximation is shown to break down for the photoionization of both inner and outer nᐉ ͑ᐉ . 0͒ electrons of all atoms, at high enough energy, owing to interchannel interactions with the nearby ns photoionization channels. The effect is illustrated for Ne 2p in the 1 keV photon energy range through a comparison of theory and experiment. The implications for x-ray photoelectron spectroscopy of molecules and condensed matter are discussed. [S0031-9007 (97)03382-6] PACS numbers: 32.80.Fb