Multiple ionization and fragmentation of negatively charged fullerene ionsby electron impact

Cross sections for the electron-impact multiple ionization and fragmentatio n of negatively charged fullerene ions C-n(-) (n = 60, 70) to C-n-m(q+) (q = 1,2, 3 and m = 0, 2, 4) have been measured for electron energies up to 1 keV. In the case of pure ionization all threshold energies are about 10 eV higher than the values expected. This shift, however, is not observed for t he fragment ions. The experimental data indicate that there is no strong el ectron-electron interaction between the incident electron and the attached electron. A novel ionization mechanism is proposed which can be expected to be valid for all negatively charged molecular or cluster ions which are ab le to shield the attached electron from the incident electron.