[en] Some new energy levels belonging to the 4f¹⁴6snp³P_0,2 series of neutral ytterbium have been measured by a three-step laser excitation technique. The spectra of the 6snp³P₂ series were analysed with MQDT. It is found that 4f¹³5d²6s³P₂ and ¹D₂ are two perturbers of the 6snp³P₂ series and the admixture coefficients of these perturbers in the bound 6snp³P₂ series were calculated. (author)

[en] Total cross sections for the production of He⁺(2p) in collisions of H⁺ and e^- with He at energies from 75 to 800 keV and from 0.8 to 7 keV respectively were measured. The ratio of the cross sections for He⁺(2p) production and for single ionization is discussed to investigate the contribution of electron correlations in the two-electron transition leading to He⁺(2p). For the first time the impact of H₂⁺ and H₃⁺ ions in comparison with H⁺ impact has also been studied for the energy range mentioned above. (author)

[en] Photon emission cross sections have been measured between 100 and 600 A in collisions of 2-105 keV amu^-1 O⁶⁺ ions on helium. The results extend existing data at low energy (0.56-7.13 keV amu^-1)to higher energy. The data are compared with the existing atomic orbital calculations for one-electron capture in (quasi-)two-electron systems. (author)

[en] A model for the evolution of charge-state distributions of fast heavy ions in solid targets is formulated, applying to the case when highly stripped ions are produced. Starting from atomic cross sections, we calculate the evolution of the individual populations in 1s, 2s and 2p subshells resulting from a dynamical competition between atomic processes like electron capture, ionisation, excitation and radiative decay processes. The final charge-state fractions are calculated by combining these individual populations. Numerical calculations are compared with experimental data for 7 MeV u^-1 Fe and 35 MeV u^-1 Kr ions in various targets. (author)

[en] The Compton profiles (CP) of H₂⁺(²Σ_g⁺) are calculated using the exact Born-Oppenheimer (BO) wavefunction for various internuclear distances R. By using the rotational-vibrational state distribution factors, calculated according to the Franck-Condon principle or measured from experiment, the vibrationally averaged values of CP for H₂⁺ and D₂⁺ in the adiabatic approximation are also calculated. Various theoretical values are given for comparison with the CP measured from H₂⁺-Ar collisions. The experimental data are compatible with the exact BO values at R = 2.0 au but the data, with an error of 15%, fail to resolve various theoretical values at either small or large momenta q. (author)

[en] By means of a continuum distorted-wave approximation of the post-collision state we derive an analytical equation for the Auger emission amplitude in ion-atom collisions. This theory includes previous models as particular cases. We further show that the presence of the projectile strongly affects the intensity profile, giving rise to a dependence on the emission angle that is missed in previous theories. In particular, a sharp enhancement in the forward direction is computed. (author)

[en] Ionisation in collisions of alpha particles with hydrogen atoms has been investigated for impact energies lying between 2 and 900 keV amu^-1. The multistate semiclassical impact parameter model with a two-centre expansion in travelling atomic orbitals was employed. The computed ionisation cross sections are, in particular in the low-energy region, in good agreement with the recent experimental data. The total and partial charge transfer cross sections have also been calculated and found to be in harmony with the available theoretical and experimental data. (author)

[en] A procedure is described for drawing a correspondence between the states and operators occurring in standard atomic shell theory and those based on a quark-like model. Quasiparticle creation and annihilation operators for electrons are expressed as coupled products of pairs of quark operators in which Dirac γ matrices make their appearance. The method is illustrated by calculating some matrix elements of single-electron tensors. (Author)

[en] The status of our knowledge on the mechanisms of multiple captures by a highly charged ion colliding with an atom is reviewed. The various and complementary techniques are first described, including energy gain spectroscopy, electron and photon spectroscopy with a particular emphasis on the rapidly developing techniques combining these spectroscopies in coincidence experiments. The double capture processes are simple enough to allow theoretical calculations and a detailed analysis of capture mechanisms such as the relative role of the electron-nucleus interaction and the electron-electron interaction. This is not yet the case for multiple captures, which imply a very large number of channels. However the simple classical overbarrier model, in its extended form, is able to account for the gross features of multiple capture processes such as the number of electrons stripped from the target. However, such models are often unable to predict the number of electrons actually captured by the projectile. (Author)

[en] Angular correlation measurements have been made of helium (e, 2e) scattering in the perpendicular plane, defined as the plane normal to the direction of the incident electron beam, at excess energies of 1, 2, 4 and 6 eV. The simultaneous analysis of these measurements with the coplanar measurements of previous authors gives the value 74±7^o for the Wannier parameter θ₀ that governs the widths of the angular correlation functions. It is also concluded that the upper limit of the excess energy for which the Wannier model is valid in helium is approximately 1.5 eV for coplanar scattering but appears to be higher for scattering in the perpendicular plane. (Author)