Reactions of Metal Ions at Fluorinated Surfaces: Formation of MF<inf>n</inf>⁺ (M = Ti, Cr, Fe, Mo, and W; n = 1-5)

Low-energy (<100 eV) ion/surface reactions of metal ions, Ti∗+, Cr.+, Fe.+, Mo.+, and W.+, at a fluorinated self-assembled monolayer surface give fluorine-containing scattered ions, MFn+, n < 5. The metal fluorides are the most abundant products in the scattered ion spectra. The single fluorine abstractions are all endothermic and driven by the projectile translational energy. Multiple fluorine abstraction occurs with high efficiency for Mo.+ and W.+ projectiles, where the thermochemistry is most favorable. Polyatomic projectile ions derived by partial fragmentation of the Cr, Mo, and W hexacarbonyls also yield metal fluoride scattered ions, in addition to more complex species formed by fluorine abstraction by ions which retain one or more carbon atoms or carbonyl groups. Fe- and Ti-containing projectile ions, bearing one or two cyclopentadienyl (Cp) groups, also exhibit fluorine abstraction products, with and without retention of a Cp group. TiCln+ (n = 1-4) projectiles exhibit fluorine abstraction, as well. Similar fluorine abstraction products are generated upon collisions at a liquid perfluorinated polyether surface. Gas-phase ion/molecule reactions and thermochemical considerations suggest that multiple fluorine abstractions can occur by a direct reaction mechanism within a single scattering event and that multiple fluorine atoms are probably derived from a single fluorocarbon chain. Angle-resolved scattering data support a single-collision, multiple-atom abstraction mechanism. The scattered ions leave the surface with very low translational energy and collision energy variations suggest that in these ion/surface reactions, projectile dissociation is concerted with or occurs prior to fluorine abstraction. There is no evidence that electron transfer to the surface is involved, as it is in alkyl group abstraction reactions by ions at hydrocarbon surfaces. © 1994, American Chemical Society. All rights reserved.