B. M. Lagutin

Photoionization of Kr near the 4s threshold. I. Experiment and LS coupling theory

Absolute cross sections for the transitions of the Kr atom into the 4s1 and 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 4s1 and 4p4nl states were also calculated, as well as the 4p4nlnl 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.

Photoionization of Kr 4s. III. Detailed and extended measurements of the Kr 4s-electron ionization cross section

Absolute Kr 4s-electron 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-electron photoionization cross sections.

Theoretical study of the Ar-3s electron photoionization and satellite production close to threshold including doubly excited states

Abstract Cross sections for photoionization of Ar-3s electrons and for satellite production were calculated near their thresholds. Moreover, energies of doubly-excited states in neutral Ar and cross sections for their population were calculated, supporting the explanation of resonance phenomena observed earlier in the 3s-electron photoionization process and in the satellite production by autoionization of doubly-excited states.

Strong impact of the giant resonance on the radiationless decay of the 4d-vacancy in Xe: II. N4, 5OO Auger effect

The radiationless decay of the Xe N4, 5 levels is investigated theoretically. The strong influence of the giant resonance in the 5s5p5(1P)ef channel on the partial and total Auger widths via the interchannel mixing is revealed. The computed widths of the N4 and N5 levels, equal to 105.9 and 109.6 meV, respectively, are in excellent agreement with the measured values 104(3) and 111(3) meV (Jurvansuu et al 2001 Phys. Rev. A 64 012502). The shape of the computed N4, 5OO Auger spectrum is in good agreement with the measured one. Interchannel interaction reduces the probability of the 5p5p − 4deg Auger decay by more than an order of magnitude. This conclusion is supported by the good agreement between computed and measured Auger electron angular distribution parameters.

Fourfold excitations, intra- and inter-shell correlations in the Auger decay of Kr 3d-np resonances

Many-electron effects in the photoionization of Kr near the 3d9np resonances were investigated theoretically. Cross sections for the population of the 4p4(1D)mp states, their alignment and orientation, and angular distribution of the Auger electrons were computed considering the resonance Auger effect as a coherent process. Probabilities of the radiative cascades following the resonant Auger effect were estimated quantitatively within the transition-array technique. The role of intra- and inter-shell correlations was investigated. Lineshapes computed, taking into account interchannel interaction, are in good agreement with the measured ones. Fourfold excitations of the Kr ground state were proposed to influence the resonance population, alignment and orientation of the 4p4np levels.

Theoretical study of photoionization of the isoelectronic sequence Rb+, Sr2+, and Y3+

The photoionization cross sections for the 4p shell of ions of the Kr isoelectronic sequence Rb+, Sr2+, and Y3+ are calculated. The configuration interaction theory and the perturbation theory are used to describe the many-electron effects. The relativistic effects are taken into account in the Pauli-Fock approximation. The calculated resonance structure of photoionization cross sections for the 4p shell in the region below the 4s threshold associated with the autoionization of the 4s-np singly excited states and the 4p4p-nln′l′ doubly excited states reproduces the results of recent measurements of total photoabsorption cross sections for the Rb+, Sr2+, and Y3+ ions. It is found that, as the nuclear charge in the isoelectronic sequence increases, the ratio between the direct and correlation parts of amplitudes of the 4s-(n/ɛ)p transition changes and, as the consequence, the minimum of the photoionization cross section of the 4s shell shifts from the continuous spectrum to the region of states of discrete spectrum. This accounts for the strong changes in the shape of the 4s-np resonances in the photoionization cross sections for the 4p shell of Rb+, Sr2+, and Y3+, as well as the distinction between the shapes of the 4s-6p1/2 mirror resonance in the partial 4p1/2 and 4p3/2 photoionization cross sections for the Y3+ ion which do not suppress each other in the total photoionization cross section, as is the case for similar resonances in Rb+ and Sr2+.

Many-electron character of Rydberg series converging to the ionization thresholds of the 4p 45s states of KrII

The photoionization cross sections of the 4p shell and the 4s main level and 4p4(3P) 5s4P5/2, 3/2 satellite subvalence levels of KrII have been calculated in the 4s-near-threshold range of excitation energies from 28.48 to 28.70 eV. The calculation takes into account the core relaxation by the methods of the theory of non-orthogonal orbitals, the interaction between resonant states through autoionization channels by solving the complex secular equation, and the interaction between the channels of the continuous spectrum in all orders of the perturbation theory by the K-matrix method. Good quantitative agreement between the energy-integrated theoretical and experimental photoionization cross sections for the satellite levels has been obtained for the first time. It is shown that only simultaneous consideration of the above-mentioned effects leads to such agreement. The resonant structure of the photoionization cross sections in this excitation energy range is related to the autoionization decay of the 4p45s(4P1/2)np and 4p45s(2P3/2)np Rydberg series. The specificity of this process is that both series manifest themselves not independently but owing to their strong electrostatic interaction with the prominent 4p4(1D)5s2D5/2 6p3/2 resonance, which lies in this excitation energy range.

Interference effects in alignment and orientation processes of atoms excited by polarized radiation

The dynamics of the processes of alignment and orientation of atoms subjected to the action of polarized radiation has been studied theoretically in the energy range of excitation of autoionization resonances. The alignment parameters A20 for the 4p45p states of Kr II populated through the excitation and autoionization decay of Kr I 3d9np resonances depend on energy due to the interference between different resonance channels and the channel of direct photoionization. It is predicted that the orientation parameter O10 of some Kr II 4p45p states and the parameter of the angular distribution of photoelectrons βe1 strongly depend on energy. The absolute photoionization cross sections are calculated for the population of the Kr II 4p45p states in the case where the energy of excitation photons corresponds to the first four 3d9np resonances. A good agreement between the calculated and measured photoionization cross sections proves that it is important to take into account the interference between different resonance channels in order to appreciate the dynamics of the Auger decay of Kr I 3d9np resonances.