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-6p1/2 resona nce line of the single-valence-electron system Yb+ have been determine d with an accuracy of about I MHz by Doppler-free saturated absorption spectroscopy in a sputtered vapor. Ab initio many-body perturbation t heory calculations in the coupled-cluster approach were then used to e valuate the electronic field shift factor, F = -14.9(2) GHzfm-2, and t o 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 str ucture constants calculated for 6s and 6p1/2 States using the same wav e functions as for the F-factor calculation and the experimentally det ermined hyperfine-structure constants. The calculated F and K(SMS) fac tors have been used to extract values for the difference in mean-squar e charge radius, delta[r2]A1,A2, between isotope pairs A1, A2, and the related nuclear charge distribution parameter lambda(A1,A2) which are just within the uncertainties of the tabulated values of Aufmuth et a l. [At. Data Nucl. Data Tables 37, 455 (1987)] based on semiempirical estimates of F and assumed values of K(SMS).