Abstract
The hyperfine structure of the 6s14d configuration of barium has been measured by optical-optical double resonance. From the observed positions for the hyperfine components of the 1D2 and 3D1,2,3 Rydberg states, the singlet and triplet character as well as the amount of admixture of the 5d7d perturbing configuration was deduced. Although agreeing qualitatively, the authors' results differ quantitatively from predictions made by multichannel quantum defect theory (MQDT).