[en] The results of recent VUV photoionization experiments of the 5d elements Ta, W, Re, Ir and Pt using atomic beam technique, excitation with monochromatized synchrotron radiation and detection of singly and doubly charged photoions are discussed. Special attention is given to the resonances caused by discrete transitions of the 5p and 4f electrons into the unfilled 5d subshells. As there is a crossover of the 5p and 4f levels along the series of the 5d elements the result is a complicated structure of the corresponding interacting resonances. The photoion spectra are compared with theoretical calculations carried out within the relativistic time dependent local density and the relativistic Hartree-Fock approximation. (orig.)

[en] We present a calculation scheme for the two-loop vacuum polarization correction of order α² to the Lamb shift of hydrogenlike high-Z atoms. The interaction with the external Coulomb field is taken into account to all orders in (Zα). By means of a modified potential approach the problem is reduced to the evaluation of effective one-loop vacuumpolarization potentials. An expression for the energy shift is deduced within the framework of partial wave decomposition performing appropriate subtractions. Exact results for the two-loop vacuum polarization contribution to the Lamb shift of K- and L-shell electron states in hydrogenlike lead and uranium are presented. (orig.)

[en] Lifetime measurements have been carried out for some low lying (n=2) levels in the four-electron ions Cl XIV and S XIII using the beam-foil technique. Accurate oscillator strengths for the 2s²¹S-2s2p¹P^o transition have been determined by the inclusion of prominent casc[es in the analysis. Lifetimes of the levels of the 2p²³P_j multiplet have also been measured for both ions. The results are compared with theoretical predictions and earlier measurements. (orig.)

[en] An analytic atomic independent-particle-model is used to generate wave functions for the valence and excited states of the neutral phosphorus atom. These wave functions are used to calculate generalized oscillator strengths, and from these quantities the cross sections are obtained in Born approximation. Various excitations from the 3p³(⁴S_3/2) ground state are considered, and results are presented for electron impact energies up to 5 keV. (orig.)

[en] The energy-pooling rate coefficient for the Ba(6s5d³D_J)+Ba(6s5d³D_J)→Ba(6s²¹S₀)+Ba(6s6p¹P₀¹) process has been measured. The barium atoms were excited by a cw diode laser tuned to the frequency of the 791.3 nm intercombination line and the metastable atoms in the 6s5d ³D_J state were produced due to radiative and collisional depopulation of the laser-excited 6s6p ³P⁰₁ state. The measurements were performed at ¹³⁸ Ba number densities of about 4 x 10¹⁰ cm^-3 and at 30 mbar argon as the buffer gas. Most of the barium ground state atoms in the excitation zone were transferred to the trip let metastable state at the laser pump power applied. The energy pooling rate coefficient was determined by comparing the fluorescence intensity of the barium 553.6 nm resonance line and the fluorescence intensity of the intercombination line 791.3 nm. In addition, the populations of the metastable atoms were probed with low intensity laser radiation from a single mode ring dye laser. The rate coefficient was found to be k = 1 x 10^-10 cm³s^-1 at T = 730 K. (orig.)

[en] The relativistic distorted-wave method was used to perform calculations for electron impact excitation of the first (np)²P_1/2,3/2 levels of Na, K and Rb at incident electron energies in the range 20-200 eV. Scattering parameters presented include differential and integrated cross sections, differential and integrated Stokes parameters, generalized STU-parameters and various collisional alignment and orientation parameters. Comparisons with experiment and other theories are in agreement except for cases where first-order methods have been previously proven to be insufficient. Relativistic effects, mainly due to the spin-orbit interaction, have been found to be prominent for rubidium. (orig.)

[en] Structure and QED effects for 2s_1/2 and 2p_3/2 levels are calculated for lithiumlike U⁸⁹⁺ trough neonlike U⁸²⁺, lithiumlike Th⁸⁷⁺ trough neonlike Th⁸⁰⁺ and lithiumlike Bi⁸⁰⁺ trough neonlike Bi⁷³⁺. The results of the first two sets are compared with recent measurements of the 2s_1/2-2p_3/2transition energy in 3 to 10-electron ions. Good agreement with experiment is found for most of the observed lines. Forty-one possible transitions are calculated for each ion in the eight ionization states, in the experimental energy range. Twenty-eight of these transitions have not been observed, nor calculated previously. We also calculate transition rates, branching ratios, excitation and ionization cross sections and confirm that the thirteen experimental observed transitions correspond to the ones with highest relative intensities. However, we find nineteen more transitions that could be measured in a more sensitive experiment. (orig.)

[en] Results of broadening and shift measurements of Doppler-free two-photon lines for transitions from the ground state to the nP_J Rydberg states with intermediate principle quantum numbers of atomic thallium perturbed by rare gases are reported. The rates show a distinct behaviour in this range of principle quantum numbers and significant dependence on the total angular momentum of the upper nP state. The experimental results are compared with calculations using a Van der Waals potential and a superposition of polarization and Fermi potentials. Additionally, broadening and shift rates of the transition Tl 6P_3/2-9P_3/2 have been measured for quadrupolar as well as for mainly scalar excitation. The rates for both kinds of excitation coincide within the limits of error reflecting the small perturbation of the 6P_3/2 state compared to that of the upper 9P_3/2 state. (orig.)

[en] The total rate coefficient k for the energy pooling process Cs^*(6P)+Cs^*(6P)→Cs(6S)+Cs^**(6D) has been measured in dependence on the ratio of the number densities of the Cs 6P fine-structure sublevels. The measurements were performed applying the laser fluorescence method. From the set of the obtained data for κ, the rate coefficients for the particular Cs^*(6P_J)+Cs^*(6P_J') collisions were derived. The obtained values for the Cs^*(P_1/2)+Cs^*(P_1/2), Cs^*(P_1/2)+Cs^*(P_3/2) and Cs^*(P_3/2)+Cs^*(P_3/2) collisions at T=600 K are κ₁=2 x 10^-9 cm³s^-1, κ₂=3.1 x 10^-10 cm³s^-1 and κ₃<3 x 10^-10 cm³s^-1, respectively. The value for κ₁ and the estimate for κ₃ are consistent with the data previously published by other authors. The rate coefficient κ₂ is reported for the first time. (orig.)

[en] We report the even parity J=4,5 autoionizing spectra of calcium below the 3d threshold, investigated by two-step laser excitation from the 3d4s metastables through the 3d4p ³F_3,4, ¹F₃ intermediate states and subsequent optogalvanic detection. The 3d4s states are populated by electronic collisions in a d.c. glow discharge sustained in a Ca heat-pipe. More than a hundred resonant transitions have been measured with an accuracy of ∝0.2cm^-1 for the narrow ones using standard laser calibration techniques. The high lying levels are assigned to all expected 3dnd J=4,5 autoionizing series. Moreover, some 3dng J=4,5 levels are observed. The theoretical interpretation is achieved by a combination of the nearly ab initio eigenchannel R-matrix and multichannel quantum-defect (MQDT) methods as well as by an empirical determination of the MQDT parameters in the phase-shifted formulation. Theoretical energy level positions and excitation profiles are compared with the experimental data confirming the identification of the observed structures. Strong mixing between 3dnd J=4 series is found, while the 3dng ones do not couple with the 3dnd series. Further insight into the strong channel mixing in the studied energy range is provided by a comprehensive review of the excitation profiles in the vicinity of the 4p5p ³D₃ perturber as obtained from a number of intermediate levels used in the present and in earlier experiments. Systematic electron correlation trends for Ndnd J=4 series of Ca(N=3),Sr(N=4) and Ba(N=5) are discussed. (orig.)