Dissociative scattering of polyatomic ions from a liquid surface: CF+3 on a perfluoropolyether film

The dissociative scattering of CF⁺₃ ions from a liquid insulating perfluorinated polyether surface was explored in the incident energy range 100-500 eV. We have measured the angular and energy distributions of the positive and negative fragment ions. The impulsive energy transfer to the liquid molecules and to internal energy of the scattered ions has been determined as a function of incoming energy and total scattering angle. The energy transfer in the ion/surface collision indicated scattering off the -CF₃ groups of the liquid molecules. The dissociation of the CF⁺₃ ions was due to a single impulsive collision with these groups. The parent ion was observed as well as CF⁺₂, CF⁺, and C⁺ ions. The degree of dissociation depends only on the total scattering angle and the incoming energy, as in gas phase scattering. Remarkably, negatively charged F^- fragment ions were also observed. These were formed in a process referred to as collisionally-induced "ion-pair" formation from neutrals leaving the surface. The important parameter which determined the internal energy uptake of the scattered ions in the collision was the translational energy loss DE the parent ion suffered. Finally, a comparison has been made between scattering from a liquid perfluorinated polyether surface and a metal Ag(111) surface.