Ion beam scattering experiments on the larger carbon molecules (C60±, C70+, C84+) demonstrate their exceptionally high stability with respect to impact-induced fragmentation processes. The charged molecules are formed by ultraviolet laser desorption of high-purity molecular samples into a pulsed helium jet. Extracted ions impact Si(100) or graphite(0001) in a high-resolution ion beam/surface collider with mass time-of-flight and angular analysis. Collisions are highly inelastic processes: A large fraction of the entire perpendicular momentum component is lost, and 60 ± 20% of the parallel component is either lost or exchanged. No more than 10% of the incident ions are returned, which is attributed to neutralization during the collision event. In contrast to all molecular ions (benzene and naphthalene cations) and clusters (alkali-metal halides), these molecules exhibit no evidence for impact-induced fragmentation, even at impact energies exceeding 200 eV. In the case of C60-, both the intact parent ion and ejected electrons are detected, with the latter becoming dominant above 120 eV impact energy. C60+ is found to have an exceptionally low energy threshold for inducing sputtering processes of adsorbed overlayers on graphite. Some of these results may be interpretable in terms of the unique structural-energetic characteristics of the fullerene family. The results are compared to recent computer simulations of the impact event, which predict high resilience for these molecules.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry