Surface impact induced shattering of C6. Detection of small Cm fragments by negative surface ionization

The efficient formation of small Cm− cluster anions (m = 2–28) is detected when mass selected C60+ cations collide with room temperature graphite, passivated silicon or tantalum surfaces at kinetic energies ranging from 300 to 1800 eV. Experimental evidence indicates that these anions are generated by negative surface ionization of small Cm fragments resulting from prompt impact induced fragmentation of the incident C60+ at the surface (shattering). This high energy process appears to be distinct from the slower metastable decay of surface scattered C60+ which leads to even numbered fullerene fragment distributions C58+, C56+, , observed at impact energies below 300 eV. A bond percolation model for C60 combined with an exponential dependence of the electron attachment efficiency on the electron affinity of the neutral Cm fragments qualitatively reproduces the observed Cm− fragment distributions for the shattering process.