State-selective single-electron stripping processes of Ar²⁺ ions in collisions with He and Ar atoms have been studied experimentally at laboratory impact energies of 6 and 8 keV by means of translational energy spectroscopy. These measurements show that the dominant reaction channels are due to ionisation of long-lived highly excited states with excitation energies very close to the ionisation potential of Ar²⁺. Weaker processes are also observed due to ionisation of metastable and ground state Ar²⁺ ions.