Optical spectroscopy of complex open-4d-shell ions Sn7+–Sn10+

We analyze the complex level structure of ions with many-valence-electron open-[Kr] 4*d*^m subshells (m=7–4) with *ab initio* calculations based on configuration-interaction many-body perturbation theory (CI+MBPT). Charge-state-resolved optical and extreme ultraviolet (EUV) spectra of Sn⁷⁺–Sn¹⁰⁺ ions were obtained using an electron beam ion trap. Semiempirical spectral fits carried out with the orthogonal parameters technique and cowan code calculations lead to 90 identifications of magnetic-dipole transitions and the determination of 79 energy ground-configuration levels, questioning some earlier EUV-line assignments. Our results confirm the ab initio predictive power of CI+MBPT calculations for these complex electronic systems.