Penning ionization of C60 molecules

A mass-spectrometric study of Penning ionization of C60 with metastable rare-gas atoms (Rg=He, Ne, Ar, Kr and Xe) shows that the sole channel is C60+ formation. The ionization cross-sections, at an average collision energy of 0.05 eV, strongly decrease from helium to xenon. The interaction potentials for C60–Rg*, C60+–Rg, C60–Rg and C60−–Rg+, and matrix elements for the coupling of the C60–Rg* and C60−–Rg+ interactions at the crossing point, have been estimated using recently proposed correlation formulas. The trend of the ionization cross-sections can be explained by the low-energy collisions between Rg* and C60, characterized by the formation of an ion-pair C60−–Rg+ intermediate with a decreasing probability on going from lighter to heavier rare gases.