2<i>s</i>-2<i>p</i>transitions in heliumlike and lithiumlike krypton

Abstract

We present a study of the 1s2s $^{3}$${\mathit{S}}_{1--}$1s2p $^{3}$${\mathit{P}}_{0,2}$ transitions in ${\mathrm{Kr}}^{34+}$ and the 1${\mathit{s}}^{2}$2s $^{2}$${\mathit{S}}_{1/2--}$1${\mathit{s}}^{2}$2p $^{2}$${\mathit{P}}_{1/2,3/2}$ transitions in ${\mathrm{Kr}}^{33+}$. Wavelengths of two- and three-electron krypton ions have been accurately measured using the beam-foil technique. The limits of precision are discussed. Our results are compared with Z-expansion and multiconfigurational Dirac-Fock theories taking account of the two-electron quantum electrodynamics (QED) contributions we have calculated for high-Z ions. The agreement is satisfactory for heliumlike ${\mathrm{Kr}}^{35+}$. However, a sizable disagreement is found for the 2 $^{2}\mathrm{P}_{1/2--}$2p $^{2}\mathrm{P}_{3/2}$ fine structure of lithiumlike Kr${3}^{6}$+, which could reflect the difficulty of calculating the QED corrections and retarded Breit interactions for three-electron ions.