Dissociative scattering of polyatomic ions from metal surfaces: CF +3 on Ag(111) and (Ba/Ag(111)

The dissociative scattering of CF⁺₃ ions from a clean Ag(111) and a barium-covered Ag(111) surface was explored in the energy range 100-600eV. Both negative (CF^-₃, CF^-₂ and F^-) and positive (CF⁺ and C⁺) ions were observed. The complete dissociation of the CF⁺₃ ions into C⁺ fragments was found at low (normal) incoming energies. 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. For the barium-covered Ag(111) surface the negatively charged scattering products only showed F^- and the positives showed CF⁺ and C⁺ fragments. No negatively charged polyatomic ions were observed. The lowering of the work function facilitates resonant neutralization into the excited 3s Rydberg state of the neutral molecule. Consequently, the spectral features associated with Auger neutralization are not observed.