Isotope shifts in ${}_{}{}^{151,153}{}_{}{}^{}\mathrm{Eu}_{}^{+}{}_{}{}^{}$ have been measured for four optical transitions between the metastable levels 4${\mathit{f}}^7$${(}^8$S°)5${\mathit{d}}^9$D${\mathrm{°}}_{\mathit{J}}$ and the excited levels 4${\mathit{f}}^7$${(}^8$S${\mathrm{°}}_{7/2}$)6${\mathit{p}}_{3/2}$;J’ in a collinear laser and slow-ion-beam apparatus. A phenomenological interpretation and an ab initio calculation have been made and compared with experiment.

• Received 14 May 1990

DOI:https://doi.org/10.1103/PhysRevA.42.2573