Photofragmentation study of core-excited NO

The production of anionic and cationic fragments of NO has been measured after photoexcitation in the vicinity of the nitrogen 1s threshold. The partial ion yield for the anionic fragment O − , in conjunction with the partial cation yields, can clearly distinguish the shape resonances from doubly excited states. On the N 1s → π* resonances, which are composed of the three intermediate states 2 Δ, 2 Σ − and 2 Σ + in the order of increasing photon energy, the intensity ratios for the NO ++ , O + and O ++ fragments are very different from the total ion yield. An explanation for this behaviour in terms of symmetry is proposed.