Single-Charge Transfer betweenHe++and He, Ne, and Ar: Observed Selection Rule for Exit Channels

Single-charge-transfer channels in the systems ${\mathrm{He}}^{++}$-He, -Ne, -Ar are observed for ${\mathrm{He}}^{++}$ energies 0.2-1.0 keV and ${\mathrm{He}}^{+(*)\mathrm{}}$ exit angles 0°-15°. (${\mathrm{He}}^{+(*)\mathrm{}}$ denotes either the ground state or an excited state.) The ground-state channels have cross sections below the present ${10}^{-20\mathrm{}}$-${\mathrm{cm}}^2$ detection limit. Outgoing channels are found to be favored when their separated ions can originate with the same molecular symmetry as the incoming channel.