Isotope shifts and hyperfine structure in the 369.4-nm 6s-6${\mathit{p}}_{1/2}$ resonance line of the single-valence-electron system ${\mathrm{Yb}}^{+}$ have been determined with an accuracy of about 1 MHz by Doppler-free saturated absorption spectroscopy in a sputtered vapor. Ab initio many-body perturbation theory calculations in the coupled-cluster approach were then used to evaluate the electronic field shift factor, F=-14.9(2) GHz ${\mathrm{fm}}^{\mathrm{-}2}$, and to estimate the specific mass shift (SMS) factor, ${\mathit{K}}^{\mathrm{SMS}}$=(1±1)${\mathit{K}}^{\mathrm{NMS}}$, where NMS is the normal mass shift. The uncertainty in the calculated F factor is based on the level of agreement between the hyperfine structure constants calculated for 6s and 6${\mathit{p}}_{1/2}$ states using the same wave functions as for the F-factor calculation and the experimentally determined hyperfine-structure constants. The calculated F and ${\mathit{K}}^{\mathrm{SMS}}$ factors have been used to extract values for the difference in mean-square charge radius, δ〈${\mathit{r}}^2$${\mathrm{〉}}_1^{\mathit{A}}$,${\mathit{A}}_2$, between isotope pairs ${\mathit{A}}_1$,${\mathit{A}}_2$, and the related nuclear charge distribution parameter ${\lambda }_1^{\mathit{A}}$,${\mathit{A}}_2$, which are just within the uncertainties of the tabulated values of Aufmuth et al. [At. Data Nucl. Data Tables 37, 455 (1987)] based on semiempirical estimates of F and assumed values of ${\mathit{K}}^{\mathrm{SMS}}$.

• Received 3 December 1993

DOI:https://doi.org/10.1103/PhysRevA.49.3351