Electron capture in collisions of O2+(3P) ions with He atoms at energies below 10 keV: The effect of metastable O2+(1D) ions.

Abstract

Electron capture in ${\mathrm{O}}^{2+}$${(}^{3}$P${,}^{1}$D)+He collisions is studied theoretically by using a semiclassical molecular representation with six molecular channels at collision energies above 50 eV and by using a fully quantum-mechanical molecular representation with three \ensuremath{\Pi} channels below these energies. The ab initio potential curves and nonadiabatic coupling matrix elements for the ${\mathrm{HeO}}^{2+}$ system are obtained from multireference single- and double-excitation configuration-interaction calculations employing a relatively large basis set. The present total cross sections for electron capture by the ground-state ${\mathrm{O}}^{2+}$ ions are found to be in reasonable accord with those calculated by Gargaud, Bacchus-Montabonel, and McCarroll [J. Chem. Phys. 99, 4495 (1993)] below 30 eV/u but are slightly larger above this energy. Partial cross sections for the l distribution are also slightly different. Cross sections for electron capture by the metastable ${\mathrm{O}}^{2+}$ ions decrease much more sharply than those for the ground-state ion as the energy is lowered, reaching a difference between them approximately as large as one to two orders of magnitude below 100 eV. The present rate coefficient for the reaction is approximately ${10}^{\mathrm{\ensuremath{-}}9}$ ${\mathrm{cm}}^{3}$/s above 10 000 K, suggesting that the small rate coefficient of about ${10}^{\mathrm{\ensuremath{-}}12}$ ${\mathrm{cm}}^{3}$/s at 20 000 K observed by Kwang and Fang [Phys. Rev. Lett. 71, 4127 (1993)] for electron capture by the ground-state ion might be caused, in part, by a mixture of ground and metastable ions in their experiment. \textcopyright{} 1996 The American Physical Society.