Impact-parameter dependence of the electronic energy loss of fast cluster projectiles

Electronic energy loss of molecular clusters as a function of impact-parameter is less understood than atomic energy loss. Vicinage effects due to mutual interference between cluster fragments play a key role in the determination of the cluster electronic energy loss. In this work, we describe a molecular extension of the perturbative convolution approximation (PCA) energy loss model, namely MPCA (molecular PCA), which yields remarkable agreement with first-order Born semiclassical approximation (SCA) results. The physical inputs of the model are the oscillators strengths of the target atoms and the projectile electron density. A very good agreement is obtained with time consuming full first-order calculations for bare incident molecular clusters for several angles between cluster axis and velocity direction.