Calculation of highly excited Rydberg states of ytterbium atoms

Asymptotically exact calculations (with n → ∞) for the positions of the Rydberg states 4f14 6s1/2nlj of Yb have been carried out. The calculations have been performed by using the relativistic-perturbation theory with a model zeroth-order approximation. The proposed approach is more universal than the usually applied quantum-defect method, and, in contrast to the latter, it does not require the availability of experimental data about the low-lying states of the considered Rydberg series. It is shown that singlet–triplet splitting increases with increasing nuclear charge, and, for sufficiently heavy atoms, this splitting may exceed the distance between adjacent Rydberg states of the same series. The results have made it possible to change the accepted interpretation of the experimental spectrum. The difference between the theoretical and experimental quantum-defect spectrum monotonically decreases as n increases and is about 0.2 for n = 45.