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 strong 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 11.48(12) meV. Convincing evidence that these states have odd parity is presented, making Os^- the only known atomic negative ion with bound states of opposite parity. Additionally, the binding energies for the Os^- ground state ( ⁴F^e_9/2) and first excited state ( ⁴F^e_7/2) are measured to be 1.077 80(12) eV and 0.553(3) eV, respectively.