Multiphoton ionization and ion-pair formation in molecular hydrogen

We have investigated both photoionization and ion-pair formation in molecular hydrogen by using double-resonance excitation via the E,F 1Σg+, v=6 level. The energetic threshold for ion-pair formation occurs just below the H2+ X 2Σg+, v+=9 ionization. threshold. The spectrum in this region was studied by using both conventional and constant-ionic-state photoelectron spectroscopy, as well as by monitoring the H- production. The decay dynamics in this region are extremely rich, because excited levels may decay by rotational and vibrational autoionization, by predissociation to neutral H + H* (n=2,3,4), by predissociation to the ion pair H+ + H-, and by fluorescence. In addition, the dissociative potential curve of the 2pσu3sσg1Σu+ doubly excited electronic state crosses the H2+ X 2Σu+ potential curve in the same energy region, and the electronic autoionization of this state is found to significantly influence these decay processes