Dynamics of the Penning Ionization of Fullerene Molecules by Metastable Neon Atoms

The collision energy dependence of the cross section for the Penning ionization of C60 molecules by metastable neon atoms has been measured in the 0.035-0.5 eV range in a crossed beam experiment. The results show a decreasing trend (∼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 intermolecular interaction: an electron transfer can be possible from the metastable rare gas atom to the C60 molecule with the formation of an ion pair collision complex. At low collision 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.