Image State Mediated Electron Transfer at Surfaces

We demonstrate that image states provide an important channel for electron transfer between an atom and a surface, especially for the excited states with comparable binding energy to that of the image states. This new channel substantially enhances the tunneling rate for, as an example, H ? on Al(111) and Cu(111), and is resonant with the (n=3) atomic level at a large separation. Such a resonance leads to charge oscillation in the scattering of H ? oo the Cu(111) surface. The prediction of these oscillations provides one way for the experimental identiication of this tunneling channel.