Item

Abstract

For the hydrogenlike Ar¹⁷⁺ ion, the 1s Lamb shift was absolutely determined with a 1.4% accuracy based on Lyman-α wavelength measurements that have negligible uncertainties from nuclear size effects. The result agrees with state-of-the-art quantum electrodynamics (QED) calculations, and demonstrates the suitability of Lyman-α transitions in highly charged ions as x-ray energy standards, accurate at the five parts-per-million level. For the heliumlike Ar¹⁶⁺ ion the transition energy for the 1s2p¹P₁→1s²¹S₀ line was also absolutely determined on an even higher level of accuracy. Additionally, we present relative measurements of transitions in S¹⁵⁺,S¹⁴⁺, and Fe²⁴⁺ ions. The data for the heliumlike S¹⁴⁺,Ar¹⁶⁺, and Fe²⁴⁺ ions stringently confirm advanced bound-state QED predictions including screened QED terms that had recently been contested.