Measurement of the metastable lifetime for the 2s^2 2p^2 ^1So level in O^2+

The radiative lifetime of the 2s22p2 1S0 level in O2+ has been measured via the magnetic-dipole (M1) transition 2s22p2 1S0 → 3P1 at 232.17 nm. Data were recorded in a Kingdon trap, with the source of ions a 14 GHz electron cyclotron resonance ion source. The lifetime of the 1S0 level was found to be 540 ± 27 ms. This is in good agreement with a previous measurement and with a number of theoretical calculations. Metastable lifetimes, when combined with collisional excitation rates, can provide a diagnostic for electron density Ne in a stellar or solar plasma.