Energy transfer and surface-induced dissociation for SiMe3+ scattering off clean and adsorbate covered metals

We scatter 10-70 eV SiMe3+ from clean Au(111), a hexanethiolate self-assembled monolayer on Au(111) (C-6), and a NiO(111) layer grown on top of Ni(111). We examine both the scattered ion fragmentation patterns and the kinetic energy distribution spectra (KEDS) as a function of the incident ion energy E. Surface infrared and KEDS data indicate that we have prepared a saturated monolayer of hexanethiolate (C-6) on Au(111) where the C-6 carbon backbone is predominantly upright on the surface. C-6 monolayers with a mixture of prone and upright C-6 can also be prepared, but only the upright C-6 monolayers are used for ion scattering experiments. The fragment ion distributions and the KEDS are then used to determine the channeling of the incident SiMe3+ ion energy into the scattered ion internal energy E-int, and the scattered ion kinetic energy E-scat. Overall, we find the order of E-int/E for SiMe3+ to be Au(111)much greater than NiO(111)>C-6. From the E-scat values, we find that MiSe(3)(+) scattering off C-6 is highly inelastic while scattering off Au is much more elastic. We use this information to calculate the energy (E-surf) which is channeled into the surface as a result of the collision for C-6 and Au(111). By comparing the KEDS for the parent and fragment ions, we determine the importance of unimolecular dissociation off the various surfaces. In the accompanying paper, we present a series of classical dynamics simulations to explain and supplement these experimental results. (C) 1997 American Institute of Physics.