Ionization rate coefficients for the elements hydrogen through zinc

Abstract

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.

Electron–ion merged-beam experiments at heavy-ion storage rings

“…A recent example for such benchmarking is the cross section for EII of Fe 14+ . Figure 2 displays the measured cross section from the TSR and the theoretical cross section from the compilation of Dere (2007). There is overall agreement concerning the gross shape and the magnitude of the cross section.…”

High-resolution solar spectral irradiance from extreme ultraviolet to far infrared

“…The optically thin ionization calculation used here will be improved in future work by adopting the consistent formulation of the dielectronic recombination/ionization provided by Dere [2007]. Also, other atomic data will be updated in the future and this includes collisional rates, increase in the number of levels, consideration of lines from more species, and more photodissociation opacities.…”

“…Also, overestimation of a few lines by factors of ∼2 occur and seem to be originated in a poor calculation of the ionization balance for a few species. The revision and more physically consistent treatment of dielectronic recombination by Dere [2007] has not yet been implemented in and will be included in future SRPM calculations.…”