Estimation of the electron affinities of C-60, corannulene, and coronene by using the kinetic method

Novel anions that contain one molecule each of C-60 and the polycyclic aromatic hydrocarbon coronene are generated in the gas phase by electron attachment desorption chemical ionization. Collision-induced dissociation reveals that these cluster ions are loosely bonded. Fragmentation of the mass-selected cluster anion yields, as the only products, the intact radical anions of the constituent molecules, namely, the C-60 radical anion and the coronene radical anion, in almost identical relative abundances. This result is interpreted as evidence that the cluster ion can be considered as the anion radical of one molecule solvated by the other molecule. The known very high electron affinity of C-60 (2.66 eV) and the comparable degree to which C-60 and the PAH compete for the electron suggests that dissociation may be controlled by the electron affinity of a portion of the C-60 surface, that is, in this case the kinetic method yields information on the ''local'' electron affinity of C-60. The electron affinity of the bowl-shaped compound corannulene is estimated for the first time to be 0.50 +/- 0.10 eV by the kinetic method by using a variety of reference compounds. Unlike coronene, corannulene reacts with C-60(-.) in the gas phase to form a covalently bonded, dehydrogenated cluster ion. Support for the concept of ''local'' electron affinity of C-60 comes from a theoretical calculation on the electronic structure of C-60 anions, which shows evidence for localization of the charge in the C-60 molecule. The possibility of electron tunneling in the C-60-coronene system is discussed as an alternative explanation for the unusual observation of equal abundances of C-60 anions and coronene anions upon dissociation of the corresponding cluster ion.