[en] Electron-impact ionization cross sections σ_q,q+n have been measured for the reaction e + Sm^q+ → Sm^(q+n) + (n + 1)e for single, double and triple ionization and initial charge states q = 1, 2, 3. The measurements have been performed using the dynamic crossed-beams technique in an energy range from the respective ionization threshold up to 1 keV. Furthermore, we have measured the single-ionization cross section for Sm¹²⁺ using the dynamic crossed- beams method and an energy-scan method. The cross sections are compared with semi-empirical formulae. In most cases the measured cross sections are described insufficiently. In the single-ionization cross section for Sm¹²⁺ a remarkable number of narrow structures resulting from resonant excitation with subsequent double-autoionization (REDA) are observed. (orig.)

[en] Electron-impact ionization of ions is one of the most fundamental processes in every kind of plasma. Especially in high-temperature plasmas-whether in laboratory (nuclear fusion) or in astrophysics (atmosphere of stars)-atoms become ionized into multiply-charged ions by electron impact. The main purpose of authors' investigations is to unravel the contributions from different ionization mechanisms-like direct ionization (one-step process), excitation-autoionization (two-step process) and inner-shell Auger processes to the cross sections of single and multiple ionization of highly-charged ions. As the experimental database is still rather small, theoretical cross sections are often used for the calculation of different plasma parameters. Cross sections for ions with an outer 4f shell are usually small and experimental data is needed in order to test theories in that region. In the present study, the authors investigate the ionization of praseodymium ions, where cross section data has not been available up to now

[en] Employing the 'crossed-beams' technique, electron-impact ionization cross sections for the single-ionization of W^q+ ions in charge states q = 1...10 have been measured. The cross sections for the ionization of ions in charge states q ≥ 5 show significant contributions below the ground-state threshold caused by the ionization of ions in excited, long-lived metastable states in the parent ion beam. In the case of W⁶⁺, the measured cross section is completely dominated by metastable contributions. For ions in charge states q = 3...7, excitation-autoionization from the ground state as well as from excited, metastable states contributes strongly to the cross sections. This results in a strong underestimation of the measured cross sections by the semiempirical Lotz formula in the energy range between the ionization threshold and the cross section maximum. (Author)

[en] Using the dynamic crossed-beams method, the following absolute cross sections σ_q,q+n for single (n=1), double (n=2) and triple (n=3) ionization by electron impact have been measured for the reaction e^-+Pr^q+→Pr^(q+n)++(n+1)e^- n=1: σ_2,3 σ_3,4σ_4,5 σ_6,7 σ_7,8 σ_8,9 σ_11,12 n=2: σ_1,3 σ_2,4 σ_3,5 σ_4,6 n=3: σ_1,4 σ_2,5 σ_3,6 The measurements have been performed in an energy range from the respective threshold up to 1 keV. For the single-ionization cross sections, contributions from excitation-autoionization processes increase with increasing charge state of the parent ion. As no theoretical calculations on praseodymium ions exist, these cross sections are compared to the semi-empirical Lotz formula [Zeitschrift fuer Physik 232 (1970) 101]. Where contributions of indirect inner-shell processes to the cross section are expected, we conducted energy-scan measurements with high energy resolution. For multiple ionization, no theoretical calculations on praseodymium ions exist. Therefore, the measured cross sections were compared to the semi-empirical formulae by Belenger et al. [J. Phys. B: At. Mol. Opt. Phys. 30 (1997) 2667] and Fisher et al. [J. Phys. B: At. Mol. Opt. Phys. 28 (1995) 3027]

[en] Electron impact ionization cross sections for the single and multiple ionization of tungsten ions have been measured by employing the ''crossed-beams'' technique. For W^q+ ions in charge states q=1...10 cross sections for single ionisation were determined. For ions in charge states q=3...7, excitation-autoionization from the ground state as well as from excited, metastable states strongly contributes to the cross sections. This results in a strong underestimation of the measured cross sections compared to the semiempirical Lotz formula in the energy range between the ionization threshold and the cross section maximum. The ionization cross section for W^q+ ions was measured in the case of double ionization for q=1...6 and of triple ionization up to q=4. The multiple ionization cross sections indicate no considerable contributions of indirect processes. (author). 17 refs, 10 figs, 1 tab

[en] Short communication

[en] Employing the animated crossed-beams technique, absolute cross sections for electron impact single ionization of the iron isonuclear sequence are measured for charge states q=1-6 for electron energies from threshold up to 1 keV, as well as for the intermediate charge states q=9,10 up to an electron energy of 5 keV. The cross sections observed for Fe^q+ ions in charge states q=1-4, 9 and 10 show a significant ionization signal below the respective ground state threshold resulting from ions in excited, long-lived metastable states in the parent ion beam. In the case of Fe⁵⁺ and Fe⁶⁺ no metastable components are found. The experimental results are in good agreement with the theoretical predictions if excitation-autoionization processes are taken into account. Our measured cross sections are also in good agreement with experimental results of other groups. (author)

[en] Electron impact ionization cross sections σ_q,q+n for gallium ions have been measured for the reaction e + Ga^q+ → Ga^(q+n)+ + (n + 1)e for single (n = 1, q = 1, 3, 8) and triple (n = 3, q = 3, 4) ionization. The measurements have been performed using the crossed-beams technique in an energy range from the respective ionization threshold up to 1 keV, partly up to 6 keV. The cross sections for single ionization of ions in the charge state q = 1 and 3 show contributions below the ground state threshold caused by ionization of ions in excited, long-lived states in the parent ion beam. The cross sections are compared with the semiempirical Lotz formula. The cross section for Ga⁴⁺ triple ionization shows contributions from inner-shell processes. Semiempirical formulae are in good agreement with the experimental data only at energies below the cross section maximum. (orig.)

[en] Absolute cross sections σ_q,q+n for the multiple ionization of C^q+, N^q+ and O^q+ ions were measured for the reactions: e + A^q+ → A^(q+n)+ + (n + 1)e. The measurements were performed for electron energies up to 6.5 keV using the animated crossed-beams method at the Giessen electron-ion crossed-beams set-up. K-shell ionization with subsequent autoionization or even double-autoionization strongly contributes to the cross sections. (orig.)

[en] Using the crossed-beams technique, cross sections for electron impact double ionization of Fe^q+ ions in charge states q=1-6 (except 2) are measured in the energy range from the respective ionization thresholds up to 1 keV, partly up to 5 keV. The data for Fe⁴⁺, Fe⁵⁺ and Fe⁶⁺ show significant contributions from inner-shell processes. Using a high-resolution energy-scan technique, we study narrow resonances in the cross sections for Fe⁴⁺ and Fe⁵⁺. Besides contributions from excitation-autoionization processes, a remarkable number of structures arising from resonant-excitation triple-autoionization processes are observed. The results are compared with the scaling laws of Fisher et al and the semiempirical formula published by Shevelko and Tawara, respectively. (author)