Electron tunneling in very low energy C 60–surface collisions: Probing normal and tangential exit velocity effects

Abstract

Normal and tangential exit velocity effects were studied for negative ion formation in collisions of very low energy ( E 0=10–40 eV) neutral C 60 molecular beams with a conducting surface. The normal and tangential velocity components of the scattered C 60 − were (1.3–5.6)×10 −4 a.u. and (0.8–3.1)×10 −4 a.u. correspondingly. The average vibrational energy per C 60 molecule was kept nearly constant for all E 0 values. The C 60 − yield was found to decrease exponentially with the inverse of the normal velocity component for both near normal and near grazing incidence angles. Practically the same slope, within experimental uncertainty, was extracted from the semilog yield plots showing that tangential velocity effects are negligible. The distance dependent electron tunneling rates from C 60 − to the conducting surface were calculated and the results were used in order to derive a characteristic distance for ion formation.