Photoionisation of atomic fluorine

The experimental ion yield curve for photoionization of atomic fluorine from the ionisation threshold (about 7.116 A) to 635 A is reported. Early members of three autoionizing series converging to the 1D2 ionic state are observed. Their peak widths are all less than the instrumental resolution (0.28 A). The largest peak, at 680.7 A, has been observed previously in emission, but surprisingly not in absorption. It is assigned to (1S0)3s, which is 'forbidden' to autoionize. An interpretation is offered, which implies superradiance or laser action from this state.