Gas-Phase C–F Bond Cleavage in Perfluorohexane Using W-, Si-, P-, Br-, and I-containing Ions: Comparisons with Reactions at Fluorocarbon Surfaces

ion of fluorine atoms occurs for each of the projectile ions examined, with up to five fluorine atoms being abstracted by W, two F atoms being abstracted in the case of CI and PCl projectiles, and just one fluorine atom being abstracted by Si, P, I, and Br-containing ions (see Table 1). The maximum numbers of atoms abstracted in ion/surface reactions are similar [26–29], although the product ion abundances are much greater than in the corresponding gas phase processes. As will be discussed further below for the charge exchange reactions, conversion of translational energy apparently assists in driving fluorine abstraction. Some of the observed reactions are endothermic but others, e.g. monoand difluorine abstraction by Pand Si-projectile ions, are exothermic as is the formation of the WF2 1z abstraction products by W (see Table 2). The thermodynamics for double fluorine pickup are dependent upon whether one or two fluorocarbon chains are involved, and whether or not new carbon– carbon bonds are formed. However, most single-fluorine atom abstraction reactions must be endothermic. (See [6] for an analogous discussion of the thermochemistry of hydrogen atom pickup reactions.) Figure 1A shows the product ion spectrum obtained upon collision of 6-eV, mass-selected W ions with perfluorohexane under single collision conditions. Note the presence of the ions WFn 1 (n 5 1–5). In addition, the presence of WCF4 1z is indicative of tungsten insertion into the C–C bond, a reaction that has been suggested to occur in ion/surface collisions [28]. Other ions in the 1160 PATRICK ET AL. J Am Soc Mass Spectrom 1998, 9, 1158–1167