Electron Capture by Multiple Charged Ions; Population of Excited States

Abstract

Both the abundance and recombination spectra of certain multiply charged ions in many astrophysical plasmas — planetary and gaseous nebulae, extended atmospheres of hot stars — may be considerably modified by charge transfer processes. While the cross sections for charge transfer in the thermal — eV energy range can, in general, be reliably estimated by the quasi-molecular model, the cross sections for electron capture into a specific excited state are still subject to much uncertainty, arising from the inability of a finite basis of adiabatic (or diabatic) states to represent the translation. It is necessary to modify the basis set either by the introduction of translation factors, if a semi-classical method is used, or by the introduction of suitable reaction coordinates, if a quantum mechanical method is used to treat the collision dynamics. Examples of the problem and possible solutions will be discussed.