Isotope shifts and hyperfine structure in the 369.4-nm 6s-6p1/2 resonance line of singly ionized ytterbium

Isotope shifts and hyperfine structure in the 369.4-nm 6s-6p_1/2 resonance line of the single-valence-electron system 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 fm^-2, and to estimate the specific mass shift (SMS) factor, K^SMS=(1+/-1)K^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 6p_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 K^SMS factors have been used to extract values for the difference in mean-square charge radius, δ<r²>^A₁,A₂, between isotope pairs A₁,A₂, and the related nuclear charge distribution parameter λ^A₁,A₂, 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 K^SMS.