Autodetaching states of H2 - and charge-transfer processes in H- on H collisions.

Abstract

A study is made of the $^{2}\mathrm{\ensuremath{\Sigma}}_{\mathrm{u}}^{+}$ and $^{2}\mathrm{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$ autodetaching states of ${\mathrm{H}}_{2}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$ from the viewpoint of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$+H, rather than the usual viewpoint of e+${\mathrm{H}}_{2}$. The model proposed in this work is a Feshbach-type formalism with two differences from previous studies. Guided by the structure of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$+H states at larger internuclear separations, Q space is defined by taking the singlet spin pair to be the pair of electrons on one center, rather than the pair of electrons in the lowest molecular orbital. These two specifications are the same at large separations, but depart from one another in the autodetaching region. It is suggested that such a Q space is more appropriate to the consideration of collisions of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ on H than are the conventional ${\mathrm{H}}_{2}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$ states obtained from the e+${\mathrm{H}}_{2}$ reaction. A second departure from previous works is the strengthening of the asymptotic condition on the Feshbach Q operator to require that 〈${p}_{r}^{2}$+V(r)〉 is less than zero for the diffuse electron, where V(r) is the full Hartree-Fock potential produced by the core, including the Hartree-Fock parts of the 1/${r}_{\mathrm{ij}}$ terms. This condition makes the diffuse electron unable to escape from the system unless it absorbs energy from the core or converts centrifugal motion into radial motion. Finally, it is shown that differential charge-exchange experiments for ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ on H can provide an experimental measurement of the energy difference between the $^{2}\mathrm{\ensuremath{\Sigma}}_{\mathrm{u}}^{+}$ and $^{2}\mathrm{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$ states and perhaps give some indication of their lifetimes as well.