A. Borovik

Absolute cross sections for photoionization of Xeq + ions (1 q 5) at the 3d ionization threshold

The photon-ion merged-beams technique has been employed at the new Photon-Ion spectrometer at PETRA III for measuring multiple photoionization of Xeq + (q = 1–5) ions. Total ionization cross sections have been obtained on an absolute scale for the dominant ionization reactions of the type hν + Xeq + → Xer + + (q − r)e− with product charge states q + 2 ≤ r ≤ q + 5. Prominent ionization features are observed in the photon-energy range 650–750 eV, which are associated with excitation or ionization of an inner-shell 3d electron. Single-configuration Dirac–Fock calculations agree quantitatively with the experimental cross sections for non-resonant photoabsorption, but fail to reproduce all details of the measured ionization resonance structures.

Electron-impact single and double ionization of W17 +

A crossed-beam setup was used to measure cross sections for electron-impact single and double ionization of W17 + ions. Absolute data and high-resolution scan spectra were obtained at collision energies ranging from threshold up to 1000eV. A comparison of the experimental results with theoretical calculations for direct ionization suggests substantial contributions of excitation–autoionization processes to electron-impact single ionization of W17 +.

Electron impact ionization of ground-state and metastable Li + ions

Direct ionization of ground-state Li+(1s21S0) and metastable Li+(1s2s 3S1) ions by electron impact has been studied in the energy range from threshold to 1000 eV using state-of-the-art experimental and theoretical approaches. Absolute cross sections obtained by crossing a beam of Li+(1s2) ions with a beam of electrons and results of convergent close coupling (CCC) calculations agree within experimental error bars of approximately 10%. Mixed beams of Li+(1s2) and Li+(1s2s 3S) ions were also prepared and apparent cross sections were measured. Good agreement with CCC theory is obtained assuming suitable fractions of metastable ions in the parent beam.

Electron-impact single ionization of Xe10 + ions

Absolute cross sections for electron-impact single ionization of Xe10 + ions have been measured by employing the crossed-beam technique in the electron–ion collision energy range from threshold up to 1000 eV. In addition, fine-step energy-scan measurements of the cross-section function have been performed revealing resonant structures associated with the excitation of an electron from inner electron subshells. For better understanding of the relative importance of direct and indirect ionization contributions to the measured cross section, configuration-averaged distorted-wave calculations have been performed. Significant contributions of indirect processes involving inner-shell excitation with subsequent autoionization could be identified. Furthermore, the calculations reveal that an ≈1% fraction of metastable ions present in the parent Xe10 + ion beam has been analysed.

Photoionization of Ne Atoms and Ne+ Ions Near the K Edge: PrecisionSpectroscopy and Absolute Cross-sections

Author(s): Muller, A; Bernhardt, D; Borovik, A; Buhr, T; Hellhund, J; Holste, K; Kilcoyne, ALD; Klumpp, S; Martins, M; Ricz, S; Seltmann, J; Viefhaus, J; Schippers, S | Abstract:

Electron impact ionization of xenon ions

We report on a comprehensive study of electron-impact single and multiple ionization of Xeq+ ions (q = 1, 2, ...,25) at energies from the observed thresholds up to 1000 eV. Special emphasis is on indirect processes and their contributions to the net ionization of the parent ion. Although this work is still in progress, it is clear that indirect processes dominate the cross sections. This is demonstrated for the example of single ionization of Xe22+ ions.

Stepwise contraction of the nf Rydberg shells in the 3d photoionization of multiply- charged xenon ions

Triple photoionization of Xe3+, Xe4+ and Xe5+ ions has been studied in the energy range 670-750 eV, including the 3d ionization threshold. The photon-ion merged-beam technique was used at a synchrotron light source to measure the absolute photoionization cross sections. These cross sections exhibit a progressively larger number of sharp resonances as the ion charge state is increased. This clearly visualizes the re-ordering of the

Plasma rate coefficients for electron-impact ionization of Xeq+ ions (q = 8, …, 17)

\epsilon

Electron-impact ionization of multiply charged tungsten ions

f continuum into a regular series of (bound) Rydberg orbitals as the ionic core becomes more attractive. The energies and strengths of the resonances are extracted from the experimental data and are further analyzed by relativistic atomic-structure calculations.

Near- K -edge single, double, and triple photoionization of

Plasma rate coefficients (PRCs) for electron-impact single ionization of ground-state Xeq+ ions () in the temperature range 2 × 105 − 2 × 107 K have been derived from a combination of experimental cross-section data and results of distorted-wave calculations. For Xe8+ and Xe9+ new measurements were performed and thoroughly analyzed with respect to the contributions from different ionization mechanisms and the effects of long-lived excited states in the parent ion beams that had been employed in the experiments. In the same manner, previously published experimental data for the higher charge states were analyzed to extract the ground-configuration ionization cross sections and to derive the associated PRCs. The resulting temperature-dependent PRC functions were parameterized and the associated parameters are provided in tabular form. With the exception of Xe8+ the absolute uncertainties of the inferred rate coefficients are estimated to be For Xe8+ the uncertainties are due to the necessary correction for strong metastable-ion contributions to the measured cross sections.