Calculations of electron-impact cross sections for the fragmentation and dissociative ionization of fullerenes using a semi-empirical method

We extended our previously developed semi-empirical method for the calculation of cross section functions (absolute value and energy dependence) for the electron-impact ionization of the neutral fullerenes C₆₀ and C₇₀, of the ionized fullerenes C₆₀^z+ (z=1-3), and of multiple ionization processes of the negatively charged fullerenes C _m^- (m=60, 70, and 84) to the fragmentation and dissociative ionization of neutral and ionized C₆₀ and C ₇₀. Measured cross sections for these processes were found to display a sharp peak in the cross section function at low impact energies which was attributed to a plasmon excitation at these energies [Phys. Rev. Lett. 85 (2000) 3604], whereas the high-energy shape of the cross sections exhibited the well-known energy dependence of a direct ionization process. The introduction of a "decay factor" in our model allowed us to separate the two contributions and we found in all cases that the plasmon contribution to the cross section exhibits a very similar shape.