A semi-empirical concept for the calculation of electron-impact ionization cross-sections of neutral and ionized fullerenes

We have developed a semi-empirical approach to the calculation of cross-section functions (absolute value and energy dependence) for the electron-impact ionization of several neutral and ionized fullerenes C₆₀^q+ (q=0-3), for which reliable experimental data have been reported. In particular, we propose a modification of the simplistic assumption that the ionization cross-section of a cluster/fullerene is given as the product of the monomer ionization cross-section and a factor m^a, where "m" is the number of monomers in the ensemble and "a" is a constant. A comparison between our calculations and the available experimental data reveals good agreement for q=0, 1, and 3. In the case of the ionization of C₆₀²⁺ (q=2), our calculation lies significantly below the measured cross-section which we interpret as an indication that additional indirect ionization processes are present for this charge state.