Measurements of translational energy gain for one- and two-electron transfer in slowArq+-He (q=15–18) collisions

We have measured n-state-resolved energy-gain distributions for single-electron capture in ${\mathrm{Ar}}^{\mathit{q}+}$-He collisions (q=15–18) at energies in the vicinity of 3.35q keV. The energy-gain scales were calibrated absolutely with precisions between a few tenths of an eV and one eV. The kinetic-energy distributions due to transfer-ionization processes (i.e., two-electron transfer followed by autoionization) were recorded and the (5,n’) series appeared to be most important for ${\mathrm{Ar}}^{16+}$. The energy-gain spectrum for true double-electron capture in ${\mathrm{Ar}}^{16+}$-He collisions, however, indicated a dominance of strongly asymmetric (4,n’) states, showing that different intermediate doubly excited states are dominant in the two processes.