Coronal lines and the importance of deep core-valence correlation in Ag-like ions

We report on large-scale and critically evaluated {\em ab initio} MCDHF calculations of the wavelength of the “coronal”, M1 transition $4f
^2$\mathrm{F}${5/2}^o-^2$\mathrm{F}${7/2}^o$ in Ag-like ions. The transition between these two fine structure levels, which makes up the ground term for $Z \ge 62$intheisoelectronicsequence,hasrecentlybeenobservedinYb$^{23+}$andW$^{27+}$, where the latter could be of great importance for fusion plasma diagnostics. We present recommended values for all members of the sequence between $Z=50$ and $94$, which are supported by excellent agreement with values from recent experiments. The importance of including core-valence correlation with the $n=3$ shell in the theoretical model is emphasized. The results show close to spectroscopic accuracy for these forbidden lines.