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.

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Resonant Auger transitions from the 3d −1 5p photoexcited states in Kr to the 4s −1 4p −1 5p and 4s −2 5p levels and subsequent Auger decay to the 4p 4 and 4s4p 5 states of Kr 2+ are studied by means of angle-resolved electron spectroscopy. The angular anisotropy parameters β are determined for most of the prominent lines in the spectrum of emitted electrons. It is found that the first-step spectator transitions are strongly anisotropic, while the secondstep participator transitions are almost isotropic. Extensive multiconfiguration Dirac-Fock calculations are performed which include correlations in all of the states involved. Noticeable improvements are achieved in comparison with early calculations. The energy position of the main spectral lines and their intensities are described satisfactorily. It turns out that the interference effects due to coherent excitation of resonances influence the anisotropy of the Auger emission significantly. The calculated β parameters agree very well with the experiment.

Symmetry-resolved photoabsorption spectra measured at the C and 0 E edges of CO have demonstrated the symmetry decomposition of the conventional photoabsorption spectra. These spectra have been compared with theoretical calculations in the K-shell ionization continua. Definite assignments for the symmetries have been given in the photon-energy regions below and above the E-shell ionization thresholds.PACS number(s): 33.80.Eh, 33.80.Gj

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Information on the structure of the ions of neon, argon, krypton and xenon dimers has been obtained using threshold photoelectron spectroscopy and synchrotron radiation under conditions of high resolution. Vibrational structure has been well resolved for the ground state of all these species thus allowing accurate values for the spectroscopic constants to be derived. Structure corresponding to excited states of the dimer ions dissociating to the 2P3/2,1/2 levels of the atomic ion have also been identified and their dissociation energies determined.

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PcL A threshold photoelectron specmm and its component spectra of Auger cascades aRer AI K-shell photoionization have been measxed by wincidenoes between threshold photoelectrons and residual ions of Lhe cascades. These spectra exhibit remarkable profiles of postcollision interaction effects due to the Auger cascades. The peak shift increases gradually according to the tims of interactions. but the peak broadening is almost indepndent of the times of interactions. Tbese p m 6 k a~ analysed in terms of a simple model expressing the pmbability of A u p eleftmu emissions by statistical w e i g hIn near-threshold inner-shell photoionization of atoms, the subsequent Auger decay might be influenced by the presence of a slowly receding photoelectron. This influence is called post-collision interaction ( F a ) .Close to the threshold, the slower photoelectron shields the doubly charged atomic ion so that the faster Auger electron gains energy and, as its counter