We report a comprehensive study of charge-exchange dynamics in collisions of $\mathrm{H}{\mathrm{e}}^{+}$ and $\mathrm{H}{\mathrm{e}}^{2+}$ ions with Ne and Ar targets at velocities ranging from 0.63 to 1.41 a.u. (atomic units). Using a high-voltage cylindrical mirror analyzer, we analyzed scattered ions at a fixed large scattering angle of 14°, achieving sub-$K$-shell penetration where projectile-target separations fall below the $K$-shell radius of the target atoms. This work bridges the gap between low-velocity quasimolecular-orbital models and high-velocity perturbative approaches. The measured $\mathrm{H}{\mathrm{e}}^{2+}/\mathrm{H}{\mathrm{e}}^{+}$ ratios exhibit a strong dependence on both velocity and target species, which are quantitatively reproduced by a modified classical overbarrier model incorporating empirical corrections for screening effects. Our analysis reveals that $K$-shell electrons dominate charge exchange at intermediate velocities due to their ultrashort orbital periods, particularly in heavy targets like Ar. Our study advances the understanding of electron dynamics in deeply penetrating ion-atom collisions and provides a valuable reference for modeling charge transfer in asymmetric systems.

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• Atomic & molecular collisions
• Electronic excitation & ionization
• Electronic structure of atoms & molecules
• Electronic transitions