ISOTOPE-SHIFT MEASUREMENTS IN CA+

We have measured the optical shifts for all stable isotopes of Ca+, with respect to isotope mass 40, in the resonance transitions 4s S-2(1/2)-4p P-2(1/2,3/2). The value of our measured shift for the even isotope mass 46 falls below the King plot. From the fit to a second King plot, omitting the shift for mass 46, we obtain a value of -312 MHz fm-2 for the field-shift constant F. A comparison of this value with ab initio calculations [G. Torbohm, B. Fricke, and A. Rosen, Phys. Rev. A 31, 2038 (1985)] and our semiempirical estimate shows better agreement when correlation effects have been included in the calculations [A.-M. Martensson-Pendrill, A. Ynnerman, and H. Warston (private communication)] and suggests that inclusion of the screening factor-beta in semiempirical methods results in an overestimate of F.