Evidence for Significant Target Outer-Shell Excitation in Multiple-Electron Capture Collisions of Slow Highly Charged Ions with Many-Electron Atoms

Unequivocal evidence for significant target outer-shell excitation accompanying multiple-electron capture, in slow collisions of highly charged ions with many-electron atoms, has been obtained by means of simultaneous Auger-electron and cold-target recoil-ion momentum spectroscopic measurements. For the 28 keV ${}^{15}{\mathrm{N}}^{7+}+\mathrm{Ar}$ collision system, it is found that target excitation accompanies about $40%$ of all double-electron capture collisions. The evidence supports the predictions of the molecular classical overbarrier model by Niehaus [A. Niehaus, J. Phys. B 19, 2925 (1986)].