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A detailed theoretical analysis of the 1s photoionization of neon is presented. It is found that the most significant many-electron correlation in computing photoionization of inner shells is the rearrangement of the outer shells caused by the inner vacancy. Further noticeable effects are: (i) the polarization of the ion core by the outgoing photoelectron and (ii) the coherent effect of double excitation/ionization. The core polarization increases the photoionization cross section by about 10% at the 1s threshold, and the coherent excitation results in further increases by about 5%. Incoherent excitation of the satellite channel leads to an additional 10% increase in the photoabsorption cross section in the double-ionization threshold region., 6 pages, 3 figures, 22 bibliography

The two-photon above-threshold 3p-ionization of argon for the photon energies exceeding the 3p-ionization threshold is studied using the correlation function technique. Generalized two-photon ionization cross sections were calculated taking into account many-electron correlations. The calculations demonstrate that the two-photon ionization of Ar at the 3p4 threshold is almost entirely a collective process. The decisive contribution in the above-threshold two-photon 3p-ionization at the exciting-photon energies corresponding to the 3p→ed giant resonance comes from the Auger-like many-electron correlations of e′ de″d − 3pef type.

Two-photon ionization of xenon was investigated theoretically for exciting-photon energies from 6.7 to 11.5 eV, which results in the ionization of Xe between $5{p}_{1/2}$ (13.43 eV) and $5s$ (23.40 eV) thresholds. We describe the extension of a previously developed computational technique for the inclusion of relativistic effects to calculate energies of intermediate resonance state and cross sections for two-photon ionization. Reasonable consistency of cross sections calculated in length and velocity form was obtained only after considering many-electron correlations. Agreement between calculated and measured resonance energies is found when core polarization was additionally included in the calculations. The presently computed two-photon photoionization cross sections of Xe are compared with Ar cross sections in our previous work. Photoelectron angular distribution parameters calculated here indicate that intermediated resonances strongly influence photoelectron angular distribution of Xe.

The dynamics of predissociation of the 2σ −1 (c 4Σ − ), v vibrational states of the O 2 + ion was studied theoretically using the method of coupled differential equations. The main equations describing the vibrational motions of nuclei in the adiabatic and diabatic approximations are given. The applicability scope of approximate methods for solving these equations was studied. The predissociation widths for the v = 0 and 1 vibrational levels were found to be Γ0 = 0.054 meV and Γ1 = 9.71 meV. This substantiated the results of recent observations of neutral fragments formed after the dissociation of the O2 molecule. About 99% of the O 2 + ions in the 2σ −1 (c 4Σ − ), v states were found to decompose to the O(1 D) + O+(4 S) dissociation products.

Photoionization cross-sections for the 4p 4 ( 3 P ) 5s 4 P 5 / 2 , 3 / 2 , 1 / 2 satellites and 4s, 4p main levels of Kr II in the exciting-photon energy range between 28.48 and 28.70 eV with extremely narrow bandwidth (1.7 meV at 28.55 eV) of the monochromatized synchrotron radiation were measured utilizing the photon-induced fluorescence spectroscopy. The observed resonances were assigned to the 4p 4 5s( 4 P 1 / 2 )n p and 4p 4 5s( 2 P 3 / 2 )n p Rydberg series on the basis of calculations performed with taking into account core relaxation and interaction between many resonances and many continua. The calculation shows that the resonance structure in the photoionization channels exists due to 4p 4 ( 1 D ) 5s 2 D 5 / 2 6 p 3 / 2 promoter state which also strongly perturbs the above Rydberg series.

Parameters of the resonant 4p 4p –3d e l Auger effect (RA) following the 3d– n p ( n = 5 , 6 ) excitation in Kr were calculated with taking into account the interference between several resonant and direct non-resonant transition amplitudes. For the first time all individual lines of the extended RA spectrum which comprises both the 4 p 4 ( 1 D ) 5p and the 4 p 4 ( 1 D ) 6p groups of final ionic states were considered. It was revealed that each group contains individual lines where the interference contributions have different signs thus providing a weak interference effect on the average over the whole group. Interference effects are found to be more pronounced in the angular distribution of the RA products.

Energy dependences of the total and partial ns-photoionization cross-sections in the vicinity of the ns-subvalence shell threshold were measured for the rare-gas atoms using photon-induced fluorescence spectroscopy. A resolution of 4.5, 3, and 1 meV was attained for Ar, Kr and Xe, respectively. The experimental cross-sections exhibit many well-resolved resonances of different shapes which are connected with the photoionization through the doubly excited atomic states. Calculated photoionization cross-sections of Ar and Kr show that some resonances are determined by doubly excited states including strongly delocalized n′f-excited electrons.

The lifetimes of the ns1 np6 2S1/2 states of Ar II, Kr II and Xe II were determined by measuring the fluorescence decay curves after selective excitation with pulsed monochromatized synchrotron radiation. The lifetimes are Ar = (4.684±0.019) ns, Kr = (30.78±0.17) ns, and Xe = (35.93±0.20) ns. Calculations performed within the configuration interaction approach show the strong dependence of the calculated lifetimes on the configuration interaction. It is proposed to use the precise lifetime values for a test of future calculations of the effective value of the Coulomb interaction of electrons.

The photoionization (PI) of the Xe atom was investigated in the vicinity of the 5s -shell threshold by photon-induced fluorescence spectroscopy. The highest resolution so far attained of 2meV enabled us to observe a new series of resonance structures in the 5s -PI cross section closely above threshold. Calculations of the partial 5s - and 5p -PI cross sections were performed taking into account many-electron correlations. These structures were related with strongly delocalized f -resonances which affect the 5s -PI cross section due to their mixing with p -resonances. {copyright} {ital 1997} {ital The American Physical Society}

A high resolution electron spectrometry study of the sub-valence 5s-photoelectron correlation satellites of Xe is presented. We report both absolute partial cross sections and angular distributions of several selected satellite lines recorded at photon energies from 40.8 eV up to 150 eV. Our high resolution results are compared to earlier lower resolution measurements and to our calculations which incorporate both configuration interaction and many-body perturbation theory techniques.

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.

Photoionization cross sections of the metastable 3P0 and 3P2 states of the 3p54s configuration of the Ar atom and 4p55s configuration of the Kr atom are calculated in one electron approximation with taking into account the many-electron correlations. It is shown, that many-electron correlations change significantly the calculated one-electron cross sections

Photoionization cross sections, σ, and angular distribution asymmetry parameters, β, for the majority of levels manifested in the subvalence ns-shell photoelectron spectra of the Kr and Xe atoms are calculated. For many levels the results of our calculations are compared with our measured σ and β values and with other works. The main mechanisms giving rise to the complex photon energy dependence of the β-parameters are analyzed.

The photoionization cross sections of the 4s-main line and the corresponding satellite lines of the Kr atom are studied experimentally and theoretically in the near-threshold region. Our measurements have been made using the photon induced fluorescence spectroscopy technique. Many-electron correlations have been accounted for in the calculations. It was shown that the interference of the direct-ionization channel and the channel of the ionization through the decay of the intermediate doubly-excited states explains the experimentally observed complex resonant structure of the 4s-photoabsorption spectrum of the Kr atom.

Photoionization cross sections of the main 2S term and satellite 2S,2P,2P0,2D terms of Ar and Kr atoms are calculated at the ns-subvalence shell ionization threshold. The calculations performed are in close agreement with the published experimental photoelectron spectra of Ar and are the basis for prediction of the subvalence shell photoelectron spectra of Ar and Kr in the 43–120 eV exciting-photon energy range.

A short review of theoretical and experimental papers devoted to the investigation of the alignment, A20, and orientation, O10, of ions after the decay of atomic resonances is presented. Special attention is paid to the dependence of A20 and O10 on the exciting‐photon energy. The possible ways for improving the theoretical description of the resonant Auger effect are also discussed.

Cross sections and angular distribution parameters for the single-photon ionization of all electron orbitals of Li2-8 are systematically computed in a broad interval of the photoelectron kinetic energies for the energetically most stable geometry of each cluster. Calculations of the partial photoelectron continuum waves in clusters are carried out by the single center method within the Hartree-Fock approximation. We study photoionization cross sections per one electron and analyze in some details general trends in the photoionization of inner and outer shells with respect to the size and geometry of a cluster. The present differential cross sections computed for Li2 are in a good agreement with the available theoretical data, whereas those computed for Li3-8 clusters can be considered as theoretical predictions.

The interaction between intermediate channels which influence the population of Kr 4p4mp ionic states in the region of the 3d9np resonances by the photon-induced Auger decay was investigated. The most important influence on the investigated process stems from 4p5'l and 3d9'l channels.

A new single-center method is proposed for solving the one-particle Schrodinger equation for molecules other than hydrides and for clusters, based on the method of associated differential and integral equations. The higher terms of the expansion of the wave function of the electron are replaced by linear combinations of analytical functions. This reduces the system of integro-differential equations to a system of differential and algebraic equations, for which stable numerical solutions have been worked out. Calculations are given of the energy and functions of the 2s state of an oxygen atom with a displaced center.