V. L. Sukhorukov

Direct Hartree-Fock calculation of the cascade decay production of multiply charged ions following inner-shell ionization of Ne, Ar, Kr and Xe

The charge spectra of multiple ions resulting from vacancy cascades in neon, argon, krypton and xenon are calculated by straightforward construction of de-excitation trees originating from various initial inner-shell vacancies. Included in the calculation are all possible radiative and non-radiative decay channels for each vacancy, and shake-off processes caused by diagram Auger, Coster-Kronig, and radiative transitions. The single-configurational Hartree-Fock approximation is employed to calculate the decay channel branching ratios and the probabilities of shake processes. The energies of levels and transition energies are calculated in the Hartree-Fock-Pauli (HFP) approximation. The dependences of level positions, level splittings, branching ratios, and shake probabilities on a configuration of a decaying ion are accounted for. Good agreement with experiment and some of the earlier calculations is obtained. The role of double electron ejection processes, other than monopole, is discussed.

Direct Hartree-Fock calculation of multiple Xei+ ion production through inner shell vacancy de-excitations

The yields of multiple Xei+ ions produced by the cascade de-excitations of the L2 to N45 inner shell vacancies are calculated with inclusion of every possible pathway of deexcitation (Auger, Coster-Kronig and radiative) at each branching point of cascade deexcitation trees. Ejections of additional electrons through shake processes are included at each step of de-excitation. Good agreement with the experiment is obtained. Simplified de-excitation schemes suggested earlier by other authors for the initial M-shell vacancies are discussed.

Single center method: A computational tool for ionization and electronic excitation studies of molecules

We discuss the recent progress in the development of the single center (SC) method for computation of highly-delocalized discrete and partial photoelectron wave continuous functions of molecules. Basic equations of the SC method are presented, and an efficient scheme for the numerical solution of a system of coupled Hartree-Fock equations for a photoelectron is described. Several illustrative applications of the method to photoionization and electronic excitation processes in diatomic molecules are considered. Thereby, we demonstrate its potential for theoretically studying angularly resolved molecular photoionization processes.

Lifetimes of the ns1 np6 2S1/2 states of singly ionized argon, krypton and xenon

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.

Angular distribution of the fluorescence radiation of Kr II satellite states

Photon-induced fluorescence spectroscopy was applied for the first time to investigate the anisotropy of VUV radiation emitted from Kr II satellite states with total angular momentum after the photoionization of the Kr atom by linearly polarized synchrotron radiation near the 4s threshold. The measurements showed that the sign of the alignment parameter is practically independent of the exciting-photon energy for the ionic state with , whereas for the states with the alignment parameter changes sign with varying energy. Simple formulae connecting the angular distribution parameter and the alignment parameter with the kinematics of our experiment and with quantities describing the dynamics of the photoionization were derived in closed form. Partial and total cross sections for the photoionization of 4p, 4s and several satellite levels were calculated taking into account many-electron correlations and doubly-excited states. For the satellite states with the dependence of the angular distribution parameter on the exciting-photon energy was calculated. Good overall agreement between theory and experiment was obtained.

Cross sections and angular distributions of the photoelectron correlation satellites of the Xe atom

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 of Kr near 4s threshold. II. Intermediate-coupling theory

The Kr 4s-electron photoionization cross section as a function of the exciting-photon energy in the range between 30 eV and 90 eV was calculated using the configuration interaction (CI) technique in intermediate coupling. In the calculations the 4p spin-orbital interaction and corrections due to higher orders of perturbation theory (the so-called Coulomb interaction correlational decrease) were considered. Energies of Kr II states were calculated and agree with spectroscopic data within less than 10 meV. For some of the Kr II states new assignments were suggested on the basis of the largest component among the calculated CI wavefunctions.

Investigation of photoionization and photodissociation of an oxygen molecule by the method of coupled differential equations

The photoionization and photodissociation of an oxygen molecule are investigated theoretically by the method of coupled differential equations. The molecular orbitals of the core are calculated in the MO LCAO approximation. The molecular orbitals of a photoelectron in the discrete and continuous spectra are determined by the single-center method. The wave functions of vibrational motion of the oxygen molecule are obtained within the diabatic approach. The described method is used for calculating the predissociation and autoionization widths of the 2σu−1(c4Σu−)n/σg, v Rydberg states of the oxygen molecule. The total cross sections of the resonant photoionization and neutral predissociation calculated for the oxygen molecule in the excitation energy range 20.6–24.8 eV are in good agreement with the available experimental data.

De-excitation dynamics of Rydberg states in O2: II. Vibrational and rotational structure of 2σ−1u(c4Σ−u)(ns/nd)σg3Σ−u(v = 0, 1) states

The competition between autoionization and neutral dissociation (ND) of the vibronic Rydberg states 2σ−1u(c4Σ−u)(ns/nd)σg3Σ−u(v = 0, 1) has been investigated using an experiment of photon-induced fluorescence spectroscopy (PIFS) and the simultaneous measurement of the photo ion yield. The experiments were performed with monochromatized synchrotron radiation from BESSY II with a very narrow bandwidth of ΔE = 1.5 meV at 23 eV where it was possible to observe single rotational branches. The experiments are compared to ab initio calculations for the partial autoionization and dissociation widths and to the corresponding simulations of the spectroscopic shape of the rovibronic branches. For more precise calculations of the dissociation widths, diabatic potential curves of the 2σ−1u(c4Σ−u) states of the O+2 are extracted from the adiabatic ones and improved calculations for molecular orbitals of the Rydberg and Auger electrons are used.

Alignment of ions after autoionization decay of atomic resonances: II. The 3d95/25p (J = 1) resonance in Kr

The alignment of the 5p4 6p levels after the decay of the Xe I 4d9 5/2 6p(J = 1) resonance was investigated experimentally and theoretically. The angular distribution of the visible fluorescence radiation was used to measure the alignment. To calculate the measured quantities the multi-step model was applied, taking account of the relativistic effects within the Pauli-Fock approximation. The influence of the cascade effects on the population of the 5p4 6p levels was estimated.