We report a direct observation of the $D$-line doublet of Na-like ions with $Z\ge 72$. Spectra in the 1–9 nm spectral range are presented showing the widely split doublet for ${\text{Hf}}^{61+}$, ${\text{Ta}}^{62+}$, ${\text{W}}^{63+}$, and ${\text{Au}}^{68+}$. The ions were produced and confined in an electron-beam ion trap and observed with a flat-field grazing incidence spectrometer. The measured wavelengths agree well with the predictions of relativistic many-body perturbation theory with QED corrections. We also report the measured wavelengths for several transitions in Si-, Al-, and Mg-like ions of Hf, Ta, and W and in Mg-like Au.

• Received 20 March 2009

DOI:https://doi.org/10.1103/PhysRevA.80.010501