Low-energy Collisions of Methane Ions at a Fluoroalkyl Monolayer Surface

Abstract

Reactive scattering of low-energy (<100 eV) CHn+ (n = 0–4) ions with a fluorinated self-assembled monolayer (F-SAM) surface produces fluorine-containing scattered ions, including CF+, C2HF2+ and C3F3+. Evidence is provided that these ion–surface reactions occur by surface-induced dissociation (SID) prior to new bond formation. Chemical sputtering of the ion-beam modified surface is consistent with the modification of the fluorinated SAM surface by the methane derived ions occurring at the terminal CF3 group. Studies with 13C-labeled ions show the formation of 12CF+ and 13CF+ in nearly equal abundance. The participation of carbon atoms arising from both the surface and the projectile suggests the intermediacy of a symmetrical fluoronium collision complex, such as [F13CF12CF]+, involving the SID fragments of the projectile and the terminal CF3 group of the surface. A 20% translational to vibrational (T → V) energy conversion is estimated from the inelastic collisions which lead to SID, a result which is consistent with previous studies using other ions on the same surface.