1 Introduction 2 Experimental methods 3 Theoretical methods 4 The H2+molecule 5 Diatomic hydride ions 6 Diatomic ions 7 The H3+ molecule 8 Polyatomic ions 9 Related processes 10 Applications

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Dissociative Recombination of Molecular Ions

Electron impact dissociation of oxygen-containing molecules A critical review

Aims. The interpretation of astrophysical spectra depends directly on a knowledge of the ionization state of the emitting plasma. This is determined, in part, from collisional ionization rate coefficients. The most recent assessments of these were performed by Arnaud & Rothenflug (1985, A&AS, 60, 425) and Arnaud & Raymond (1992, ApJ, 398, 394). Since their work, new laboratory measurements of ionization cross sections have become available as well as the Flexible Atomic Code (FAC) which enables theoretical calculations of these rates. Our goal is to provide a complete set of ionization rate coefficients for the elements hydrogen through zinc. Methods. A scaling law, which assists the analysis of ionization cross sections and rate coefficients, has been developed following the approach of Burgess & Tully (1992, A&A, 254, 436). Essentially all available measured cross sections along each isoelectronic sequence have been examined and compared to cross sections calculated with the Flexible Atomic Code (FAC) and with other calculations. Two approaches has been taken to provide a complete set of ionization cross sections. In the first, fits to scaled measured ionization cross sections, particularly for neutral and singly ionized species, are performed. In the second, fits to scaled calculated direct ionization and excitation-autoionization cross sections are performed to provide the remainder of the set. The fits to the cross sections are then integrated over a Maxwellian velocity distribution to derive ionization rate coefficients. Results. A complete set of ground level ionization cross sections and rate coefficients has been developed through the combination of these two approaches. A tabulation of parameter fits to ground level ionization rate coefficients for all atoms and ions of the elements of H through Zn is provided.

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Ionization rate coefficients for the elements hydrogen through zinc

We review the development of the time-dependent close-coupling method to study atomic and molecular few body dynamics. Applications include electron and photon collisions with atoms, molecules, and their ions.

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The time-dependent close-coupling method for atomic and molecular collision processes

Electron–ion collisions are among the most important atomic processes in ionized gases. They comprise elastic scattering, excitation, ionization, and recombination. Theoretical approaches are numerous but calculating reliable results for applications is a task that has not generally been solved, although theory has progressed considerably in the last decade and can now provide reference data for electron collisions with few-electron systems. Experimental data on electron–ion collisions can be inferred from plasma observations, from ion trap measurements, from careful preparation and analysis of ion–atom collisions, and from colliding-beams experiments. The spectrum of equipment employed in the measurements ranges from table top size to large accelerator and storage-ring facilities. This article provides an overview of the processes involved in electron–ion collisions, their cross sections, the experimental approaches and typical results. The present status of the field is discussed and characterized by numerous examples illuminating the accomplishments as well as the limitations of experimental access to accurate detailed cross sections and rate coefficients, as they are required for understanding and modelling laboratory or astrophysical plasmas.

Electron–ion collisions: Fundamental processes in the focus of applied research

New absolute cross section measurement for the reaction H- + e --> H+ + 3e- is reported for interaction energies from threshold to 2 keV by using the animated crossed beam method. The present results confirm the disagreement between the previous results of this laboratory and the results of Peart et al.

The formation of H+ from H- by electron impact

The first absolute cross section measurements for single and double electron impact ionization of sodium-like Ar7+ are reported. The animated crossed beams method has been employed in the energy range from threshold to 3000 eV. The measured cross sections for single ionization are higher than the theoretical and semi-empirical predictions by about 20-50%. This discrepancy has been associated with the contribution of the indirect ionization processes. The double ionization cross section is only 1% of the single one.

Absolute Cross-section Measurements for Electron-impact Ionization of Ar-7+

Measured cross sections for single ionisation of Li-like N4+, O5+ and Ne7+ by electron impact are reported for energies from threshold to 2500 eV. The animated crossed beams method has been employed. In addition to direct ionisation, the 1s22s to 1s2l2l' excitation followed by autoionisation is shown to give a significant contribution to the total cross section, and its magnitude has been estimated for all three ions. Comparisons are made with other experimental results and different theoretical predictions. Cross sections for N4+ and O5+ are in a good agreement with previous results and the first result on Ne7+ ionisation is well reproduced by the Coulomb-Born calculations.

Absolute Cross-section Measurements for Electron-impact Ionization of Li-like N-4+, O+5+, and Ne-7+ Ions

A new crossed beams apparatus for measuring absolute electron impact ionization cross-sections of multiply charged ions is described. First measurements are also reported which deal with N/sup 4+/ and N/sup 5+/. The results are in good agreements with those previously obtained by the Oak Ridge group, For N/sup 5+/ a non-negligible signal is observed below the ground state ionization threshold. It is attributed to the presence of ions in metastable states. From the semi-empirical Lotz formula the population of ions in those states is estimated to be approximately 3%.

Electron impact ionization of N 4+ and N 5+

Absolute cross sections for electron impact ionization and dissociation of CO2+ to form C+ and O+ fragments are measured in the energy range from threshold to 2500 eV. The animated crossed-beams method has been employed. The ionization cross section shows a maximum of 4.79 x 10(-17) cm(2) at 130 eV and the corresponding threshold is found in good agreement with previous measurements. Both dissociation cross sections are shown to exhibit wide plateaux which are of the same order of magnitude. In addition, these cross sections almost coincide above 100 eV. The threshold energy and kinetic energy released are determined for both the production of C+ and O+. They are found in good agreement with the previously published data obtained in electron impact ionization experiments of neutral CO2.

https://iopscience.iop.org/article/10.1088/0953-4075/34/9/312/pdf

S. Rachafi

Papers

The formation of H+ from H- by electron impact

Absolute Cross-section Measurements for Electron-impact Ionization of Ar-7+

Absolute Cross-section Measurements for Electron-impact Ionization of Li-like N-4+, O+5+, and Ne-7+ Ions

Electron impact ionization of N 4+ and N 5+

Electron impact ionization and dissociation of CO2+ to C+ and O+