Measurements of electron multiplicity spectra in coincidence with reflected projectiles for well defined angles of incidence (typically ψ ≤ 5°) allow for the first time to unambiguously separate contributions from potential and kinetic electron emission in HCI-surface interactions. From such measurements we could demonstrate that potential electron emission is solely dependent on the vertical component of the impact velocity. Molecular dynamics calculations performed in order to simulate the interaction of projectiles with ideal as well as rough surfaces help to understand characteristic differences in the number of emitted electrons for surface channeled projectiles and those undergoing scattering in collisions with surface imperfections.