On atomic collision processes at low impact parameters

The thesis presents experimental results obtained during the last decade in inner-shell ionization studies at the Bucharest Tandem accelerator. All data are corrected for multiple ionization effects, by using outer-shell ionization probabilities determined from energy and intensity shifts of the X-ray lines and some simple calculations in the independent electron approximation. There are included: (i) L-subshell vacancy production cross section ratios L1/L2 and L2/L3 of thorium bombarded with Be, C, F, Mg, Si and S ions at 0.5-2.5 MeV/u energy. They reveal the intra-shell vacancy sharing during the collision, as a function of the ion type and energy, and could be qualitatively explained in a two-step model; (ii) Projectile K-shell and target L3-subshell ionization cross sections and 3 dσ molecular orbital (MO) vacancy production and sharing estimates in the collision system Ni+Pb at 0.25-1.75 MeV/u bombarding energy. The integral probability of 3 dσ-2 p3/2σ MO vacancy sharing could be explained in the simple two state Nikitin approximation only at low velocities, and the 3 dσ production cross section could be estimated in a semiclassical approximation, in the united-atom limit, providing the binding energy is properly taken into account; (iii) 3 dσ single and double vacancy production and sharing probabilities in the collision system Ni(1.5 MeV/u) + Pb, as a function of the impact parameter in the range of 500-4000 fm. A strong variation of the P(2)/P(1) ratio of double to single vacancy production as a function of the impact parameter (from about 10% at 500 fm to 1% at 4000 fm) was found and qualitatively interpreted as illustrating the dominant TS2 (two step projectile-electron) mechanism of double ionization. (author) 62 figs., 8 tabs., 144 refs