Excitation of multipole plasmon resonances in clusters by fast electron impact

We demonstrate that the electron energy loss spectrum in collision with metal clusters or fullerenes depends strongly on the scattering angle of the electron. This results from the fact that the excitation probability of the surface plasmon modes of different multipolarity is correlated with the scattering angle of the electron. We derive the kinematic conditions under which the plasmon excitation with the given angular momentum dominates in the cross section. We perform our treatment in the resonance plasmon approximation and also in the random phase approximation with exchange using the wavefunctions of the Hartree-Fock jellium model. We compare the predictions of these two quite different approaches for the cluster Na-40 and report their qualitative agreement. Theoretical results are compared with the available experimental data for the electron-fullerene C-60 collision. Reasonable agreement between theoretical and experimental results is reported.