Level shifts ofmsnsRydberg states induced by hyperfine interaction in odd alkaline-earth isotopes

Abstract

High-resolution two-photon spectroscopy was applied to investigate the msns ${}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ Rydberg states of the alkaline-earth elements Ca, Sr, and Ba. It is shown for ${}_{}{}^{43}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{87}{}_{}{}^{}\mathrm{Sr}$, ${}_{}{}^{135}{}_{}{}^{}\mathrm{Ba}$, and ${}_{}{}^{137}{}_{}{}^{}\mathrm{Ba}$ that the hyperfine interaction causes a level shift between odd- and even-mass isotopes. A theoretical interpretation is presented which relates the energy-level shift for odd isotopes to the singlet-triplet separation which in turn is a function of the principal quantum number, and good agreement with the experimental results is found.