Measuring the radiative decay of metastable states
Light emitted by the spontaneous decay of metastable states is collected from highly charged ions isolated in a unitary Penning trap. The fine structure for some ions with large nuclear charge Z can have level spacing in the optical domain. We study the metastable 2P3/2 state in boron-like Ar XIV, which decays to the 2P1/2 ground state via a spin flip accompanied by emission of a λ ~ 441 nm photon. This forbidden transition in the 1s22s22p1 fine structure of Ar13+ is an interesting process for benchmarking few-electron atomic theory.