The collisional energy dependence of the cross section for the Penning ionization of C60 mols. by metastable neon atoms was measured in the 0.035-0.5 eV range in a crossed beam expt. The results show a decreasing trend (.apprx.20%) in the low-energy range up to 0.06 eV, with a slightly increasing dependence in the higher energy range. This behavior is interpreted in terms of the characteristics of the intermol. interaction: an electron transfer can be possible from the metastable rare gas atom to the C60 mol. with the formation of an ion-pair collision complex. At low collisional energy the system evolves mainly adiabatically and the ionization occurs mainly from the ion-pair complex. However, at higher collision energies, nonadiabatic transitions become possible and the systems can remain partially "trapped" within the higher adiabatic state with a consequent increase of the ionization probability. [on SciFinder (R)]