Interference effects in Stark spectra of weakly autoionising 5dnf states of barium

Weakly autoionising 5d3/2nf Rydberg states of barium around n=60 have been studied in the presence of a static electric field. The experiment has been carried out in a CW laser-atomic-beam setup. In between the overlapping n=60 and 61 angular momentum manifolds broad 5d63d resonances interact with the manifold states resulting in pronounced interferences. These interferences (anti-crossings) have been analysed by a direct diagonalisation procedure neglecting interactions with the continuum, and by a multichannel quantum defect theory analysis including continuum interactions. (orig.). With 9 figs., 1 tab