ION SURFACE COLLISIONS AT FUNCTIONALIZED SELF-ASSEMBLED MONOLAYER SURFACES

Collisions of polyatomic projectile ions at surfaces which bear a variety of organic functional groups result in the scattering of ions which have incorporated groups picked up from the surface. The reactions observed include abstraction of atoms and groups such as H., F., CH3. and C2H3.. Dissociative ion/surface reactions are also observed; in these, the initial adduct fragments by loss of radical species such as H. or F., or loss of a stable neutral molecule such as H-2, HCN or HF. The strength of the C-F bond is suggested to be the reason why closed-shell ions, such as the phenyl cation, are observed to form fluorine addition products, whereas the corresponding hydrogen atom abstraction process is not observed. Surface-induced dissociation (SID) also shows a strong dependence on the nature of the surface. At one extreme is the fluorinated surface, which is a particularly ''hard'' surface, being effective at transferring projectile translational energy into internal energy. Metal carbonyl ions serve as thermometer molecules to measure translational to internal energy transfer, and experiments with Cr(CO)6.+ and W(CO)6.+ allowed the distribution of internal energy deposited in the projectile ion to be measured. Under typical conditions, the average energy transferred was some 12-19% of the laboratory energy of the projectile, with the higher value corresponding to the fluorinated surface and the lower value to the hydrocarbon surface. The amount of energy taken up by the target in a typical case was approximately 60% of the projectile laboratory energy. The fluorinated surface is also the most efficient among those studied in the total yield of scattered ions produced relative to the projectile ion current. The carboxylic acid terminated alkanethiol is the least efficient of the surfaces studied, whereas the deuterated, hydroxyl, nitrile and ester-linked ferrocene show intermediate behavior. These results indicate that the fluorinated surface has special value in the SID experiment,