M-Shell Dielectronic Recombination: Theoretical Study

Dielectronic recombination (DR) is an important atomic physics process that is relevant to astrophysical plasma modeling. DR is responsible for the charge state balance as well as the cooling of plasmas, and it is the dominant electron-ion recombination process for most ions in both photoionized and collisionally-ionized plasmas. Accurate and reliable calculations for DR rate coefficients are needed to analyze the spectra obtained from astrophysical observations. Over the past few years, our group has computed reliable DR and radiative recombination (RR) data for all isoelectronic sequences up through Mg-like ions using a state-of-the-art multi-configuration Breit-Pauli (MCBP) approach. Recently, we have focused our work on the complex third-row M-shell isoelectronic sequences, especially Al-like. Although there exist some DR calculations for S3+, those calculations were performed only within a non-relativistic LS-coupling approximation and for electron-ionized, higher temperatures. Fe13+ DR calculations have been completed and tested against the Heidelberg heavy-ion Test Storage Ring facility measurements. Semi-relativistic DR cross section and rate coefficient calculations for Al-like S3+ using the level-resolved distorted-wave AUTOSTRUCTURE program will be presented. The effect of ground-state fine structure on the DR rates will be discussed. These calculations include final-state-resolved partial DR and RR rate coefficients from the initial ground and metastable levels spanning a temperature range of 10 z2 K-107 z2 K, where z is the initial ionic charge. Our computed Maxwellian DR rate coefficients are fitted into a simple formula for efficient dissemination of data and ease of use in plasma modeling codes, and comparisons to existing data will be shown.