Observation of Circular-Metastable Doubly Excited States of Barium

Using the adiabatic crossed-field method we have prepared for the first time doubly excited barium atoms with one valence electron in an oriented circular Rydberg state (n=21, l=m=20, denoted 21c) and the other electron in a ${6\mathrm{p}}_{\mathrm{j}}$ state. In a fraction of these atoms the inner electron decays radiatively to a ${5\mathrm{d}}_{\mathrm{j}\prime }$ metastable level. The obtained circular-metastable doubly excited atoms are very stable. For the (${5\mathrm{d}}_{3/2>\mathrm{}}$21c) state the autoionization lifetime τ is longer than 400 μs; for the (${5\mathrm{d}}_{5/2}$21c) state, τ=1±0.2 μs. the specific role of the 5d electron is demonstrated. © 1990 The American Physical Society