Search for outer-well states above the ionization potential in H2

Abstract

Abstract Recent ab initio calculations by Detmer et al. [J. Chem. Phys. 109 (1998) 9694] and by Staszewska and Wolniewicz [ J. Mol. Spectr. 212 (2002) 208] have produced potential energy curves in the energy region between the n=3 and n=4 dissociation limits in hydrogen, that in principle support bound states of an exotic nature. They are confined to large internuclear separation (R>10 a.u.) by a potential barrier giving the H2 molecule an unusually large size. In an experimental study involving a four-laser excitation scheme such states were searched for, but the dominant feature observed in this energy region is that of a direct continuum excitation when probing states of ungerade symmetry. An analysis in terms of a Landau–Zener tunneling model predicts that all vibrational levels in the 6 1 Σ + u state, perhaps with exclusion of the v=0 level, are subject to rapid predissociation.