FORMATION AND CHARACTERIZATION OF C60HE+

It is shown that kiloelectronvolt collisions of C60+ with helium result in not only the expected dissociation to yield smaller fragment carbon cluster ions but also the formation of fullerene-helium adduct ions corresponding to C(x)He+, where x is even and varies from 48 to 58, in agreement with Schwarz et al. This report provides the first unambiguous identification of the C60He+ product, indicating that the helium adduct formation does not require fragmentation. By use of hybrid tandem mass spectrometric techniques the mechanism of the formation of these unusual adduct species was investigated. The nature of the collisions, the energies of the process, and the products of dissociation of C60He+ provide strong evidence that the helium atom is inside of the fullerene cage structure.