%0 Generic
%A Bekker, Hendrik
%D 2016
%F heidok:20759
%R 10.11588/heidok.00020759
%T Optical and EUV spectroscopy of highly charged ions near the 4f–5s level crossing
%U https://archiv.ub.uni-heidelberg.de/volltextserver/20759/
%X In recent years, various highly charged ions (HCI) with optical transitions have been proposed for metrology and searches of a possible variation of the fine-structure constant α. Optical transitions in HCI are uncommon due to the scaling of energy levels with atomic number Z^2 . At the 4f–5s level crossing, three configurations are nearly degenerate, and thus many optical transitions can exist. The complex many-electron couplings reduce the accuracy of  current calculations. Moreover, experimental data to benchmark the predictions is lacking. Spectra in the optical and extreme-ultraviolet (EUV) range of several ion species near the 4f–5s level crossing were measured at the Heidelberg electron beam ion trap. A collisional-radiative model was employed for the interpretation of the EUV data, resulting in the first identification of the long sought-after 5s–5p transitions in Pm-like Re^14+ , Os^15+ , Ir^16+ , and  Pt^17+. The characteristic line shapes of optical transitions in Ir17+ were studied, with the aim of identifying transitions with a high sensitivity to α-variation. Previously suggested candidates could be excluded and new candidates were proposed. This data provides a stringent benchmark for state-of-the-art precision atomic theory.