Abstract Electronic polarization induced by low energy ions near solid surfaces at grazing incidence considerably modifies the collision geometry. This effect is studied by the comparison between experimental and simulated time of flight (ToF) spectra of helium ions scattered from amorphous Si for small incidence and emergence angles. In this work, we include the image effect and the external stopping power in a simulation code through the Specular Reflection Model (SRM). The image potential is computed by using the dielectric surface functions in the Random Phase Approximation (RPA), Plasmon Line Approximation (PLA) and static Thomas–Fermi approximation. With the later, it is found a better agreement with the experiment for the ionic part of the spectra.