Collision Strengths of Astrophysical Interest for Multiply Charged Ions

Abstract

The electron impact excitation and ionization processes are crucial for modeling the spectra of different astrophysical objects, from atmospheres of late-type stars to remnants of supernovae and up to the light emission from neutron star mergers, to name just a few. Despite their significance, however, little is known quantitatively about these processes for low- and medium-impact energies of, say, Ekin≲5000 eV of the free incident electron. To further explore the role of impact excitation, we here expanded Jac, the Jena Atomic Calculator, to the computation of distorted wave collision strengths for fine-structure-resolved, as well as configuration-averaged transitions. While we excluded the formation of dielectronic resonances, these tools can be readily applied for ions with a complex shell structure and by including the major relativistic contributions to these strengths. Detailed computations of the collision strengths are shown and explained for the impact excitation of lithium- and chlorine-like ions. When compared with other, well-correlated methods, good agreement was found, and hence, these tools will support studies of effective collision strengths for a wide range of electron impact energies, levels, and ionic charge states.

Rapid Access to Empirical Impact Ionization Cross Sections for Atoms and Ions across the Periodic Table

“…These measurements also show that at low impact energies, the inner-shell excitation of the 2s + 2p (and to a minor extent, the 1s) shells plays a relevant role owing to the rapid autoionization of these hole configurations. These inner-shell excitation also explains the various "jumps" in the total EII cross section in terms of the excitation thresholds and the contributions from the different shells [59]. The role of these excitation-autoionization processes is also seen in the rather large deviations of all empirical models for impact energies below and near the maximum of the total cross section.…”

Generalized binary-encounter-Bethe model for electron impact ionization of atoms

“…The discrepancy in the lower energy range likely arises from omitting the excitation-autoionization contributions [54][55][56] in the present model. The difference between the present computations and experiment mainly arise from autoionization contributions due to the excitation of the 5p and 5s electrons into autoionization states with thresholds (12.256 46 and 20.9515 eV for the 5p and 5s electrons, respectively [57,58]) near the corresponding ionization potentials of each orbital.…”