Molecular ion-pair states in ungerade H2

Molecular ion-pair states are analogs of electronic Rydberg states, but with the electron replaced by a much heavier ion. We calculate ab initio the long-range vibrational H+H- ion-pair states in H-2 for ungerade (1)Sigma(+)(u) symmetry, corresponding to recent observations by Ekey and McCormack [Phys. Rev. A 84, 020501 ( 2011)]. The overall trends in the experiment are reproduced and many peaks can be assigned. The calculations yield interloper resonances corresponding to vibrational states trapped inside the barriers on the potential-energy curves 5,6(1)Sigma(+)(u).