No abstract available

[en] The dynamics of many-particle quantum systems is still one of the most important unsolved problems in quantum physics. For three-electron escape from an ionic potential close to the fragmentation threshold theories predict a symmetric electron emission with 120 relative angles as well as a T-shape emission with two electrons emitted back-to-back and the third one emitted perpendicular. We have realized such a strongly correlated three electron continuum in electron impact double ionization of helium atoms. Kinematical complete experiments were performed for impact energies 27 eV and 5 eV above the break-up threshold. For the higher energy (27 eV) symmetric as well as T-shape configurations are observed

No abstract available

No abstract available

[en] The single ionisation of water molecules by 95 eV electrons has been studied in a kinematically complete experiment. By employing a seeded supersonic beam vibrationally and rotationally cold H₂O molecules were accessible in the gas phase. The distributions of momenta for electrons and ions after the ionisation were measured using the reaction microscope technique. For non-dissociative ionisation of water fully differential cross-sections (FDCS) could be obtained. Additionaly the dissociative ionisation channel leading to OH⁺ and H was investigated. Dependencies of the cross sections on the emission angle of the OH⁺ ions were found

[en] Fully differential cross-sections (FDCS) for electron impact ionization of simple molecules have found increased interest over the last years. However, up to now no experimental data has been available for aligned molecules. Using an advanced reaction microscope we performed a kinematically complete experiment where the momentum vectors of all final state particles were determined. The alignment of the molecular axis was derived from post-collision dissociation of the residual ion. Results are presented for two distinct reaction channels: Ground-state ionisation and autionisation.

[en] Reaction microscopes (RM) deliver kinematically complete information on atomic and molecular ionization processes. We want to extend this method to the investigation of excitation, e.g. by charged particle impact. By means of a laser pulse the excited states are photoionized and the released electron and the ion are detected. From the energies and angular distributions of these particles we gain detailed information on the primary collision process. Examples for electron impact excitation of atoms are presented

[en] The investigation of single and multiple ionization of atoms by electron impact allows insight into the dynamics of fundamental few-body quantum systems. In the past we have performed these studies combining a standard thermo-cathode electron beam source with a Reaction Microscope (see, e.g., Duerr et al., PRL 96, 243202). In future we aim to improve the electron beam quality concerning the energy definition and timing structure. We therefore have built a photoemission source based on a semiconductor cathode with negative electron affinity (NEA). The design, the preparation procedure of the GaAs crystal and the resulting beam properties will be presented

[en] The dielectronic recombination (DR) resonances for highly charged ions have been investigated through measurements of ions extracted from the Heidelberg electron beam ion trap (EBIT) while slowly scanning the electron energy. At strong DR resonances, the yield of the He-like krypton ions was substantially reduced, whereas that of the Li-like krypton ions was correspondingly increased. At slightly higher electron energies similar features were observed for the Li- and Be-like krypton ions. The DR process can be therefore used to modify significantly the ion charge state distribution, and by judicious choice of the excitation and recombination energies and timing, to concentrate the extracted ion current into particularly interesting charge states while depleting the undesired ones. This is particularly important for future charge breading experiments with short-lived radioactive isotopes, in order to improve the total charge breeding efficiency and to reduce the radioactive ion beam losses in the accelerator system. The convenient control of this parameters in an EBIT makes them well suited for this purpose

[en] The investigation of single and multiple ionization of atoms by electron impact allows insight into the dynamics of fundamental few-body quantum systems. In the past we have performed these studies combining a standard thermo-cathode electron beam source with a Reaction Microscope (see, e.g., Duerr et al., PRL 96, 243202). In future we aim to improve the electron beam quality concerning the energy definition and timing structure. We therefore have built a photoemission source based on a semiconductor cathode with negative electron affinity (NEA). The design, the preparation procedure of the GaAs crystal and the resulting beam properties will be presented