The M1 ground state fine structure transition in Ag-like Yb

In our previous work, the agreement between the theoretical and measured wavelength for the 4f-M1 transition of Ag-like W shed light on the importance of a careful treatment of all core-valence correlation effects to obtain a reliable value of this fine structure energy separation. To confirm these results and extend the analysis isoelectronically, we have undertaken an experimental and theoretical study of the same M1 transition in Ag-like Yb. The measured wavelength for this M1 transition is 515.77 ± 0.10 nm (515.91 nm in vacuum) which agrees well with our ab initio theoretical value of 515.48 nm. (paper)