Surface Scattering of Hyperthermal (10–50 eV) C60 Molecules: Kinetic Energy Transfer, Vibrational Excitation, and Initial Vibrational Energy Effects

Abstract

AbstractScattering of neutral C60 molecules from surfaces at hyperthermal impact energies of 10–50 eV was studied as a function of impact energy, scattering angle, surface temperature, and incident vibrational energy. Scattered kinetic energy scaled linearly with impact energy, and kinetic energy losses varied with scattering angle from ∼85% to ∼40% (peak values). Analyzing the results, we found nearly complete decoupling between normal and tangential energy losses. Tangential losses are described in terms of various models of rotational excitation and it is concluded that translational slip is involved during the scattering process. The C60 surface interaction well‐depth was determined from the scattering results and compared with the measured desorption energy. Using a newly developed vibrational thermometry method for C60 we measured kinetic energy losses and collisional vibrational excitation as a function of the average vibrational energy of the incident C60 (<Ev> = 7–15 eV). Kinetic energy loss was independent of initial vibrational energy for both near‐grazing and near‐normal scattering angles, while collisional vibrational excitation showed a weak inverse dependence on initial vibrational energy for both scattering angles. For the lowest incident C60 vibrational energy (<Ev> = 9.8 eV) and near‐normal scattering (30.7 eV in the normal impact energy component), vibrational excitation was 5% of the impact kinetic energy. Our detailed results describe the first real “bouncing” regime for C60 scattering off surfaces.