Resonant Ionization Spectroscopy ofBa−: Metastable and Stable Ions

A new technique based on the combination of laser photodetachment and resonance ionization spectroscopy has been used to characterize the state composition of a fast, negative-ion beam of barium and to determine the binding energies of its long-lived components, the metastable $5d6s6p{}_{}{}^4{}_{}{}^{}F_{9/2}^{}{}_{}{}^{}$ state and the ${6s}^{2}6p{}_{}{}^2{}_{}{}^{}P_{3/2,1/2}^{}{}_{}{}^{}$ ground state, with an accuracy previously inaccessible for the weakly bound, negative alkaline-earth ions. Additional information about the ${\mathrm{Ba}}^{-}$ states was obtained from lifetime studies in the ASTRID storage ring.