Calculation of absolute electron-impact ionization cross-sections of dimers and trimers

We report calculations of the electron-impact ionization cross-sections of selected dimers (homonuclear diatomic molecules) and trimers (homonuclear triatomic molecules) using a method which relies only on macroscopic quantities in conjunction with a "defect concept". The empirically determined defect describes the deviation of the cluster (dimer, trimer) cross-sections from a simple linear dependence on the cluster size. We compare the calculated cross-sections to experimental data for the dimers S-2 and F-2 and the trimer O-3 and we present predictions for the ionization cross-sections of Br-2, I-2, C-2 and C-3 for which no experimental data are available. Lastly, we extend the method to the calculation of ionization cross-sections for the fullerenes C-60 and C-70.