SURFACE SCATTERING OF HYPERTHERMAL (10-50 EV) C-60 MOLECULES - KINETIC-ENERGY TRANSFER, VIBRATIONAL-EXCITATION, AND INITIAL VIBRATIONAL-ENERGY EFFECTS

Scattering of neutral C-60 molecules from surfaces at hyperthermal imp act energies of 10-50 eV was studied as a function of impact energy, s cattering angle, surface temperature, and incident vibrational energy. Scattered kinetic energy scaled linearly with impact energy, and kine tic energy losses varied with scattering angle from similar to 85% to similar to 40% (peak values). Analyzing the results, we found nearly c omplete decoupling between normal and tangential energy losses. Tangen tial losses are described in terms of various models of rotational exc itation and it is concluded that translational slip is involved during the scattering process. The C-60 surface interaction well-depth was d etermined from the scattering results and compared with the measured d esorption energy. Using a newly developed vibrational thermometry meth od for C-60 we measured kinetic energy losses and collisional vibratio nal excitation as a function of the average vibrational energy of the incident C-60 ([E-v] = 7-15 eV). Kinetic energy loss was independent o f initial vibrational energy for both near-grazing and near-normal sca ttering angles, while collisional vibrational excitation showed a weak inverse dependence on initial vibrational energy for both scattering angles. For the lowest incident C-60 vibrational energy ([E-v] = 9.8 e V) and near-normal scattering (30.7 eV in the normal impact energy com ponent), vibrational excitation was 5% of the impact kinetic energy. O ur detailed results describe the first real ''bouncing'' regime for C- 60 scattering off surfaces.