On the tensor polarizabilities in the 4fN 6s2 ground levels of the neutral rare-earth atoms

A systematic study of the Stark splitting of the 4fN 6s2 ground levels in the lanthanides was performed by the nonlinear level-crossing technique and the optical pumping method with rf detection in parallel electric and magnetic fields. The tensor polarizabilities of the hyperfine structure levels in 141Pr I, 159Tb I, 165Ho I, 169Tm I and of the fine structure levels in 142Nd I, 164Dy I, and 166Er I were deduced from the level-crossing and rf signals. Values of the tensor polarizability of the 4f electron were evaluated from the experimental results. On average these values decrease with the increasing number of 4f electrons from the value of 141Pr (4f3 6s2) α2(4f) = 1.16(12) kHz/(kV/cm)2 to the value of 169Tm (4f13 6s2) α2(4f) = 0.68(4) kHz/(kV/cm)2. This decrease is caused by the lanthanides contraction. (orig.)