<title>Competition among autoionization, predissociation, and ion-pair formation in molecular hydrogen</title>

Abstract

We have investigated autoionization, predissociation, and ion-pair formation fromlhi_hly + excited states of molecular hydrogen by using double-resonance excitation via the E,F lT.g, v=6 level. The energetic threshold for ion-pair formation occurs just below the _ X 2)".;, v+=9 iomzation threshold. The spectrum in this region was studied by using conventional and constant-ionic-state photoelectron spectroscopy, by monitoring the H" production, and by detecting dissociation products by ionization with a third laser. The decay dynamics in this region are extremely rich, because the 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 2pOu3SOg _I;+ doubly excited electronic state crosses the H_ X 2T._ potential curve in the same energy region, and the electronic autoionization of this state is found to significantly influence these decay processes.