Many-body treatment of the photon emission process in electron-cluster collisions

We present the results of the many-body treatment of the bremsstrahlung (BrS) process in collisions of fast electrons with metal clusters. We concentrate our attention on the range of photon frequencies characteristic for plasmon excitations in clusters. The dynamic polarizability of a cluster in this frequency range is very large and it determines the value and behaviour of the cross section of the process as a function of various parameters. When calculating the cross section of the process, we treat the dynamic response of the cluster in the random-phase approximation with exchange, using wavefunctions of the Hartree-Fock jellium model and also in the resonance plasmon approximation. The latter approach is well applicable for the treatment of collective excitations of electrons in clusters. We analyse the spectral and angular distributions of the emitted photons, as well as the collision velocity dependence of the cross section for small sodium clusters and demonstrate that collective electron excitations determine the main features of the BrS cross section.