Detailed Atomic Structure of Neutral and Near‐Neutral Systems

This paper highlights the issues which need to be addressed in undertaking accurate calculations of multi-electron atoms and ions, particularly at or near the neutral end of an isoelectronic sequence. We illustrate the processes through two calculations - of transitions in CI I and Sn II - and discuss the convergence of our results as well as updating previous work. In particular, in the case of CI I, we propose new identifications of the levels involved in certain transitions which are important in determining the abundance of chlorine in the inter-stellar medium (ISM), while in singly ionised tin, our calculations suggest a re-evaluation of the the abundance of tin in the ISM. We also confirm recent identification of Sn II lines seen in tokamak plasmas.