Lifetimes of F2+ and Cl2+ in the A2Πu state

The PIFCO technique,in which mass-selected photoion-fluorescence photon coincidences are counted, is used to determine the lifetime of the A2Πu state of F2+ and Cl2+. Values of 1.4 μs (F2+) and 0.54 μs (Cl2+) are measured, and they are compared with lifetime measurements by other methods. The F2+ result is used to determine the electronic transition moment Re of the A2Πu-X2Πg transition to be 0.51 au, in excellent agreement with ab initio calculations. Oscillator strengths of the A-X transitions of all fluorescing halogen cations are evaluated, and the results discussed.