[en] The calculation of autoionizing resonances in atomic photoionization by use of many-body perturbation theory is discussed. Calculations of resonance structure are presented for photoionization cross sections of chlorine, manganese, and helium. In the case of helium, the cross section for photoionization with excitation to n = 2 levels is presented as well as the asymmetry parameter β which describes the angular distribution of the photo-ejected electrons. Detailed comparisons are made with experimental results. 45 references, 7 figures, 1 table

[en] The R-matrix approach to the description of autoionization in photoionization is outlined. Recent developments allowing the photoionization of excited states and heavy atoms to be considered are illustrated by calculations carried out over the last few years. The near term prospects of the method are discussed. 18 references, 5 figures

[en] In many-electron atoms with open shells strong autoionization resonances occur when an electron from an inner, weakly bound subshell is excited. Usually, the resonance state lies above several ionization thresholds and, hence, will decay into more than one exit or continuum channel. Several cases are discussed in which the resonance state is induced by synchrotron radiation, and the exit channels are differentiated and characterized by the analysis of the ejected electrons. 10 references, 6 figures

[en] Most of the rules for atomic or molecular autoionization have been derived within a two-channel model, involving one open channel (the continuum) and one closed channel (the discrete states). Very often, especially in molecules, autoionization processes involve additional coupled channels, open or closed, which complicate the resonance features by violating the two-channel rules. As an example the authors discuss the case of complex resonances, due to the autoionization of a Rydberg series close to its ionization threshold, perturbed by an isolated discrete state. 14 references, 5 figures

[en] Molecular autoionization may be modeled as the coupling of the quasi-continuum channel of Rydberg states with the continuum channel of ionization states. This model is used to describe the autoionization of H₂, HI, and CH₃I. 19 references, 2 figures

[en] The results of a systematic investigation of electronically autoionizing Rydberg states in HCl are discussed. Vibrationally resolved photoelectron spectroscopy was used to map out the non-radiative decay of vibronic levels of 3psigma → n(/sub d//sup s/)sigma Rydberg states converging to the A²Σ⁺(3psigma)^-1 excited ionic state. The observed vibrational distributions of the resulting X²PI(1π)^-1 ionic state are compared with the results of model calculations of Terwilliger and Smith based on spectral analysis of the absorption spectrum. Overall, the X²PI vibrational branching ratios are found to be in only rough qualitative agreement with the calculations and these results are discussed in relation to the approximations involved. 18 references, 5 figures

[en] Two aspects of autoionization rooted in molecular behavior are discussed. The first is the implications for autoionization in two-electron systems of strong, molecule-like correlation of the outer electrons, particularly the implications for the angular distribution of photoelectrons. The second aspect is the vibrationally-induced autoionization of small polyatomic molecules. Here the microscopic theory of vibrational autoionization is cast in a simplified form to emphasize the various physical origins of different contributions to the bound-free coupling, and then the implications of this theory are explored to distinguish the way stretching and bending modes induce the coupling. 8 references, 5 figures

[en] Calculation of the radiationless as well as the radiative decay rates for the 2p⁴(¹S)3s ²S state are given. For comparison purposes, similar calculations for the 2P⁴(¹D)4s ²D state are made. The calculation is based on the multi-configuration Dirac-Fock (MCDF) method. A spin-orbit interaction is built in, this method is capable of studying LS forbidden Auger transitions. 9 references, 1 table

[en] The comparison of the photoionization efficiency (PIE) spectrum for Hg⁺ from Hg and those for HgX₂⁺, X = Cl, Br, and I, shows that prominent autoionization Rydberg series observed in the PIE spectra for these mercury dihalide and their fragment ions can be assigned to transitions, which are mainly associated with the mercury atom in HgX². Autoionization resonances observed in different fragment ion channels are found to exhibit different Beutler-Fano line profiles. An attempt was made to fit the autoionization resonance profiles using the Fano line shape formula. 21 references, 4 figures, 5 tables

[en] This paper describes recent results in laser excited-state photoelectron spectroscopy for autoionization of NO molecule. Emphasis is placed on advantages of this technique, a promising new method for studying superexcited states. The autoionization occurs through Rydberg states. 6 references, 6 figures