CLEAVAGE OF C-C AND C-F BUNDS BY XE-DOT AND I+ IONS IN REACTIONS AT AFLUORINATED SELF-ASSEMBLED MONOLAYER SURFACE - COLLISION ENERGY-DEPENDENCE AND MECHANISMS(CENTER)

Collisions of Xe+. with a fluorinated self-assembled monolayer surface cause C-C and C-F bond cleavage as evidenced by the reactively scatte red ions XeCF2+., XeCF+, and XeF+. The projectile ion extracts difluor ocarbene from the fluorocarbon to form XeCF2+. in a low-energy reactio n, while simple fluorine abstraction also occurs and yields XeF+ in a higher energy but entropically favored process. The intact trifluorome thyl iodide radical cation, ICF3+., resulting from simple C-C cleavage , is observed as a scattered product when I+ is chosen as projectile, as are analogous ions IF+., ICF+., and ICF2+, resulting from C-F and C -C bond cleavage with concomitant I-F and I-C bond formation. Multiple F-atom abstraction occurs in a single collision evidenced by the prod uct, IF2+. Density functional theory calculations confirm that the rea ctions that lead to XeF+ and XeCF+ are more endothermic than XeCF2+. f ormation. The experimental observations and enthalpy calculations sugg est that two reaction pathways contribute to XeF+ formation: oxidative insertion at low collision energy and formation of a fluoronium ion ( -F+-) at high collision energy. The generation of XeCF2+. products is also accounted for through an oxidative insertion mechanism. Although chemical sputtering, i.e., charge exchange with liberation of fluoroca rbon cations from the surface, also occurs even at very low collision energy, it does not appear io contribute to the formation of ion/surfa ce reaction products discussed.