Tensor polarizabilities of the 4f 7(8 S)5d6s 2 9 D 2,3,4,5,6 levels in Gd I

Abstract

The optical pumping method with rf detection and the nonlinear level crossing technique were used in parallel electric and magnetic fields to investigate the Stark splitting of all the fine structure levels of the ground multiplet 4f7 (8S) 5d6s29D in Gd I. The tensor polarizabilities were deduced from the level crossing and the rf signals. The variation of the tensor polarizabilities is well reproduced by the LS coupling approximation, except for the small value of the9D5 level. A value of the tensor polarizability of the 5d electron is evaluated from the experimental results, α2(5d)=2.00(6) kHz(kV/cm)2. It is shown that the ratio between the electric quadrupole constant and the tensor polarizability is constant, except for the9D5 ratio, which is caused by a breakdown of the central field model.