Ionic-covalent problem in the ${\mathrm{H}}^{+}$+${\mathrm{H}}^{-}$⇄${\mathrm{H}}^{*}$+H collisional system

A detailed theoretical study of ${\mathrm{H}}^{+}$+${\mathrm{H}}^{-}$⇄${\mathrm{H}}^{*}$+H collisions in the $0.02<\mathrm{}{E}_{\mathrm{c}.\mathrm{m}.\mathrm{}}<10\mathrm{}$ keV energy range is reported. Calculations of the relevant states of the quasimolecular system are carried out at large internuclear distances ($5a_0<R<\mathrm{}100\mathrm{}{a}_0$) with a model involving only the loosely bound electron of the system. Our calculated adiabatic states agree well with the available accurate ab initio results. Diabatic states are found not only to differ from the conventionally invoked pure ionic and covalent states, but also to depend dramatically on the choice of the fixed electron coordinate origin. Such differences show up in the cross-section calculations when ${\mathrm{H}}^{*}\mathrm{}(n=3\mathrm{})+\mathrm{H}$ channels are taken into account and demonstrate the need for considering the problem of the electron translation factor. Cross-section calculations are finally calculated in a 12-state projected valence-bond diabatic basis incorporating a common translation factor of the Schneiderman-Russek type. The results demonstrate the important contribution of ${\mathrm{H}}^{*}\mathrm{}(n=3\mathrm{})+\mathrm{H}$ channels to the mutual neutralization process. Good agreement is obtained with the experimental data on neutralization and detachment in ${\mathrm{H}}^{+}$+${\mathrm{H}}^{-}$ and on ${\mathrm{H}}^{+}$ formation in ${\mathrm{H}}^{*}\mathrm{}\left(2s\right)+\mathrm{H}$, for collision energies $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}\gtrsim 200$ eV. At lower energies no explanation of the structures and magnitude of the experimental neutralization cross section is found.