Collisions of hyperthermal oxygen atoms, with an average energy of 500 kJ mol-1, on a series of 1-Cn-3-methylimidazolium tetrafluoroborate (n = 4, 8, 12) ionic liquids were studied with the use of a beam-surface scattering technique. Detection of inelastically scattered O atoms and reactively scattered OH and H2O recoiling from the surface at various angles and velocities revealed a vast amount of detailed information about the dynamics of energy exchange and reactions between O atoms and the ionic liquids. The data showed significant differences between the scattering from the three related ionic liquids that differ only in the length of the alkyl chain bound to the imidazolium cation. This change in composition is demonstrated by the experiments to have a substantial effect on the interfacial structure and chemistry of the ionic liquids: the ionic liquid containing the long alkyl chains has a larger tendency to locate these moieties at the surface, which affects its behavior in collisions with gases. The scattering dynamics of O atoms and the OH and H2O reaction products become more similar to their scattering behavior on a pure alkane surface as the length of the alkyl chain increases. Theoretical calculations of the surface structure corroborate the structural information gleaned from the experiments. A fundamental knowledge of how gases react with and dissolve in room-temperature ionic liquids will aid in the development of applications of ionic liquids where gas-surface interactions are important.  The figure shows a cross-sectional snapshot near the vacuum-liquid interface of 1-butyl-3-methylimidazolium tetrafluoroborate.

Scattering dynamics of hyperthermal oxygen atoms on a series of ionic liquid surfaces: [C4mim][BF4], [C8mim][BF4], and [C12mim][BF4]

248th National Meeting (2014)

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