Charge Exchange-induced X-Ray Emission of Fe xxv and Fe xxvI via a Streamlined Model

Charge exchange (CX) is an important process for the modeling of X-ray spectra obtained by the Chandra, XMM-Newton, and Suzaku X-ray observatories, as well as the anticipated Astro-H mission. The understanding of the observed X-ray spectra produced by many astrophysical environments is hindered by the current incompleteness of available atomic and molecular data—especially for CX. Here, we implement a streamlined program set that applies quantum defect methods and the Landau-Zener theory to generate total, n-resolved, and n{\ell }S-resolved cross sections for any given projectile ion/target CX collision. By using these data in a cascade model for X-ray emission, theoretical spectra for such systems can be predicted. With these techniques, Fe²⁵⁺ and Fe²⁶⁺ CX collisions with H, He, H₂, N₂, H₂O, and CO are studied for single-electron capture (SEC). These systems have been selected because they illustrate computational difficulties for high projectile charges. Furthermore, Fe xxv and Fe xxvi emission lines have been detected in the Galactic center and Galactic ridge. Theoretical X-ray spectra for these collision systems are compared to experimental data generated by an electron-beam ion trap study. Several ℓ-distribution models have been tested for Fe²⁵⁺ and Fe²⁶⁺ SEC. Such analyses suggests that commonly used ℓ-distribution models struggle to accurately reflect the true distribution of electron capture as understood by more advanced theoretical methods.