Low-energy collisions of methane ions at a fluoroalkyl monolayer surface

Abstract

Reactive scattering of low-energy (<100 eV) CH_n⁺ (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.