ENERGY DISPOSAL AND TARGET EFFECTS IN HYPERTHERMAL COLLISIONS OF FERROCENE MOLECULAR-IONS AT SURFACES

Ferrocene molecular ions undergo inelastic collisions at Si(100) and a lkanethiol self-assembled monolayer surfaces (SAMs). Dissociation of t he activated projectile follows its recoil from the surface; viz., sur face-induced dissociation (SID) occurs by a two-step mechanism, and th e fragmentation pattern is independent of the nature of the surface. O n the other hand, the SID efficiency for collisions at the SAM surface s is much greater than that for the Si(100) single-crystal surface as a result of a decrease in neutralization at the organic surfaces. The fragmentation pathways of a ferrocene molecular ion are elucidated as a function of collision energy and presented as energy-resolved mass s pectra (ERMS) on the SAM and Si(100) surfaces. Translational to vibrat ional energy partitioning is similar for Si(100) and a hydrocarbon sur face (ca. 13%) but greater for a fluorocarbon surface (ca. 20%). The f errocene molecular ion displays a high SID efficiency (total scattered ion yield) on the organic surfaces compared to other common projectil e ions due to its low ionization energy. Because charge exchange betwe en the projectile molecular ion and the surface is minimized, ferrocen e does not undergo ion/surface reactions.