Stark effect in barium6sndD21Rydberg states; evidence of strong perturbations in theF31series

The scalar and tensor polarizabilities of the barium $6snd$ ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ states with principal quantum number $n$ ranging from 14 to 30, as well as those of the $5d7d$ ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ perturber state near $n=26\mathrm{}$, have been measured with high-resolution laser-atomic-beam spectroscopy. The data are analyzed by calculating the contribution to the polarizabilities of all known odd-parity states connected via the electric dipole operator with the ${}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ states. In this way the contributions of the unknown $6snf$ ${}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ states are inferred. The results indicate that the ${}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ series is heavily affected by at least two perturber states. A tentative three-channel quantum-defect—theory analysis of the ${}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ series, based on a fit to the experimental polarizabilities, is presented.