EXCITATION OF MULTIPOLE PLASMON RESONANCES IN CLUSTERS BY FAST-ELECTRON IMPACT

We demonstrate that the electron energy loss spectrum in collision wit h metal clusters or fullerenes depends strongly on the scattering angl e of the electron. This results from the fact that the excitation prob ability of the surface plasmon modes of different multipolarity is cor related with the scattering angle of the electron. We derive the kinem atic conditions under which the plasmon excitation with the given angu lar momentum dominates in the cross section. We perform our treatment in the resonance plasmon approximation and also in the random phase ap proximation 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 agreeme nt. Theoretical results are compared with the available experimental d ata for the electron-fullerene C-60 collision. Reasonable agreement be tween theoretical and experimental results is reported.