Covalent-ionic problem: H+-H- ion pairs from doubly excited (H2)** formed by transfer-excitation of H+2 during collisions

We measured the laboratory energy distribution of H+-H- pairs in coincidence, at 0 with respect to the beam direction, produced by 4.0 keV H+2 colliding with Xe and He. The transformation of the laboratory energy distribution of H+-H- pairs in coincidence from the laboratory frame to the center-of-mass frame shows that, contrary to the earlier measurements, the charge transfer to the dissociative excited H2 state releases a substantial amount of maximum kinetic energy (∼ 4 eV/ion) which suggests that H+-H- pairs result from the dissociation of doubly excited states of H2. These doubly excited states of H**2 are formed by an electron transfer-excitation process which is studied in molecules for the first time. The energies of these doubly excited states have been calculated by Guberman and are consistent with our measurements of the H+-H- energies. The dissociation process proceeds from covalent doubly excited states through states of mixed doubly and singly excited configurations, to states of mixed ionic and covalent configurations, to a final pure ionic state. The details of this transformation are still open to conjecture and await further theory and calculations. (orig.)