Surface-induced dissociation from a liquid surface

Abstract

Mass-selected projectile ions in the tens of electronvolt energy range undergo surface-induced dissociation upon collision with a liquid perfluorinated polyether (PFPE) surface. The efficiency of translational-to-vibrational (T-V) energy transfer is simiar to that observed for a fluorinated self-assembled monolayer (SAM) surface. The thermometer ion W(CO)^+·₆ was used to determine an average T-V conversion efficiency of 18% in the collision energy range of 30-50 eV. The surface can be bombarded for several hours without displaying any change in the scattered ion products. Ion-surface reactions occur with some projectiles and are analogous to those seen with the fluorinated SAM surface. For example WF⁺| (m = 1-5) and W(CO)_nF⁺| (n = 1-2, m = 1-2) are generated upon collisions of W(CO)^+·₆ with the PFPE liquid surface. The ion-surface reactions observed suggest that F atoms and / or CF₃ groups are accessible for reaction while the oxygen atoms lie below the outermost surface layer. Chemical sputtering of the liquid surface also occurs and yields common fluorocarbon fragment ions, including CF⁺₃, C₂F⁺₇ and the oxygenated product CFO⁺. The liquid surface is remarkably free of hydrocarbon impurities. Collisions of the pyrazine and benzene molecular ions, both probes for hydrocarbon impurities, resulted in very little protonated pyrazine or protonated benzene.