Journal of Chemical Physics, Vol.106, No.24, 10329-10336, 1997
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.
Keywords:ORGANOSULFUR COMPOUNDS;IMPULSIVE EXCITATION;ORGANIC-SURFACES;GOLD SURFACES;IONS;CHEMISORPTION;COLLISIONS;MONOLAYERS;AU(111);AU