Ion-molecule charge exchange: He+ and Ar+ on H2 and N2

Abstract

Charge exchange in ${\mathrm{He}}^{+}$ and ${\mathrm{Ar}}^{+}$ collisions with ${\mathrm{H}}_2$ (${\mathrm{D}}_2$) and ${\mathrm{N}}_2$ is studied at small angles. This work extends our earlier studies which primarily emphasized the direct inelastic scattering at low keV energies. Using time-of-flight techniques for energy analysis of the scattered atoms, it is directly shown, for the first time, that in ${\mathrm{Ar}}^{+}$ + ${\mathrm{H}}_2$, ${\mathrm{Ar}}^{+}$ + ${\mathrm{N}}_2$, and ${\mathrm{He}}^{+}$ + ${\mathrm{N}}_2$ the dominant small-angle charge-exchange process is quasiresonant ($Q\approx 0$). In ${\mathrm{He}}^{+}$ + ${\mathrm{H}}_2$ there is no available quasiresonant channel, and here the dominant final channels are associated with energy losses from 13 to 18 eV. A simple model is proposed.