Dissociation of polyatomic ions at surfaces: The influence of mechanical and electronic energy transfer.

Abstract

The dissociative scattering of ${\mathrm{CF}}_{3}^{+}$ ions from a clean Ag(111) surface was explored in the energy range 100--600 eV. Both negative (${\mathrm{CF}}_{3}^{\mathrm{\ensuremath{-}}}$, ${\mathrm{CF}}_{2}^{\mathrm{\ensuremath{-}}}$, and ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$) and positive ions (${\mathrm{CF}}^{+}$ and ${\mathrm{C}}^{+}$) were formed. The complete dissociation of the ${\mathrm{CF}}_{3}^{+}$ molecular ions into ${\mathrm{C}}^{+}$ fragments was found to be feasible at low (normal) incoming energies. We conclude that the breaking of three C-F bonds is due to concerted electronic and mechanical energy transfer. The azimuthal orientation of the crystal has a large influence on the degree of dissociation, which indicates the importance of direct momentum transfer. \textcopyright{} 1996 The American Physical Society.