DISSOCIATIVE SCATTERING OF POLYATOMIC IONS FROM METAL-SURFACES - CF3+ON AG(111) AND BA AG(111)/

The dissociative scattering of CF; ions from a clean Ag(lll) and a bar ium-covered Ag(lll) surface was explored in the energy range 100-600 e V. Both negative (CF3-, CF2- and F-) and positive (CF+ and C+) ions we re observed. The complete dissociation of the CF3+ ions into C+ fragme nts was found at low (normal) incoming energies. The breaking of three C-F bonds is due to concerted electronic and mechanical energy transf er. The azimuthal orientation of the crystal has a large influence on the degree of dissociation, which indicates the importance of direct m omentum transfer. For the barium-covered Ag(111) surface the negativel y charged scattering products only showed F- and the positives showed CF+ and C+ fragments. No negatively charged polyatomic ions were obser ved. The lowering of the work function facilitates resonant neutraliza tion into the excited 3s Rydberg state of the neutral molecule. Conseq uently, the spectral features associated with Auger neutralization are not observed. (C) 1998 Elsevier Science B.V.