High resolution spectroscopy on 6sns Rydberg states of barium

Extensive new data on perturbed and unperturbed levels of the 6sns 1S0 and 6sns3S1 Rydberg series of Barium have been obtained in a high-resolution laser atomic-beam experiment. Special attention has been paid to the region above n=15 where the 3S1 series is strongly perturbed. The results on hyperfine energies and isotopic fieldshift ratios are compared with calculations using wavefunctions obtained from a Multi Channel Quantum Defect analysis. The applicability of various approximations to these wavefunctions is discussed. Good agreement between experiment and calculation is obtained. (orig.)