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

Recent ab initio calculations by Detmer et al. [J. Chem. Phys. 109 (1998) 96941 and by Staszewska and Wolniewiez [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 H-2 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(\)Sigma(u)(+) state, perhaps with exclusion of the tau = 0 level, are subject to rapid predissociation. (C) 2002 Elsevier Science B.V. All rights.