Experimental studies of Os-: Observation of a bound-bound electric dipole transition in an atomic negative ion

The first experimental studies of Os- reveal the presence of two very stron g resonances. One state is a narrow shape resonance lying only 3.52(12) meV above the ground state detachment threshold, while the other is bound by 1 1.48(12) meV. Convincing evidence that these states have odd parity is pres ented, making Os- the only known atomic negative ion with bound states of o pposite parity. Additionally, the binding energies for the Os- ground state (F-4(9/2)e) and first excited state (F-4(7/2)e) are measured to be 1.07780 (12) eV and 0.553(3) eV, respectively.