Identifications of $5{{{\rm s}}_{1/2}}-5{{{\rm p}}_{3/2}}$ and $5{{{\rm s}}^{2}}-5{\rm s}5{\rm p}$ EUV transitions of promethium-like Pt, Ir, Os and Re

Abstract

We investigated Pm-, Nd-, and Pr-like spectra in the extreme ultra-violet region around 20 nm of Pt, Ir, Os, and Re (Z = 78–75) produced in the Heidelberg electron beam ion trap. Identification of the transitions was supported by several theoretical calculations, including collisional radiative modeling of the observed spectra. Special attention is given to the identifications of the alkaline-like – resonance lines in promethium-like highly charged ions. Previous identifications of these lines have been tentative at best due to disagreements with theory and doubts about the experimental charge state identifications. Our experimental results for the – wavelengths are accurate at the 0.005%-level. Understanding the level-structure of ions near the – level crossing is of particular importance for future searches of a possible fine-structure constant variation, and new optical clocks.