Estimation of the electron affinities of C60, corannulene, and coronene by using the kinetic method

Novel anions that contain one molecule each of C60 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 C60 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 C60 (2.66 eV) and the comparable degree to which C60 and the PAH compete for the electron suggests that dissociation may be controlled by the electron affinity of a portion of the C60 surface, that is, in this case the kinetic method yields information on the local electron affinity of C60. 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, denydrogenated cluster ion. Support for the concept of "local" electron affinity of C60 comes from a theoretical calculation on the electronic structure of C60 anions, which shows evidence for localization of the charge in the C60 molecule. The possibility of electron tunneling in the C60-coronene system is discussed as an alternative explanation for the unusual observation of equal abundances of C60 anions and coronene anions upon dissociation of the corresponding cluster ion.