From kinetic energy measurements in an ICR cell, the charge-transfer reaction between thermal He+ and O2 is shown to produce 64% of ground state O+ ions with 1.8 eV kinetic energy, and 36% of electronically excited O+* with 0.3 eV kinetic energy. These O+* react with O2 with a rate constant of 6.5 × 10-10cm3s-1. The nature of this excited state, 2D° or 2P°, is discussed. A resonant, long-distance electron jump explains all the experimental data. © 1979 American Institute of Physics.