Superthermal Al Atoms as a Reactive-Atom Probe of Fluorinated Surfaces

[Image: see text] We demonstrate a proof-of-concept of a new analytical technique to measure relative F atom exposure at the surfaces of fluorinated materials. The method is based on reactive-atom scattering (RAS) of Al atoms, produced by pulsed laser ablation of solid Al at 532 nm. The properties of the incident ground-state Al were characterized by laser-induced fluorescence (LIF); at typical ablation fluences, the speed distribution is approximately Maxwellian at ∼45000 K, with a most-probable kinetic energy of 187 kJ mol(–1) and a mean of 560 kJ mol(–1) When these Al atoms impact the surfaces of perfluorinated solids (poly(tetrafluorethylene), PTFE) or liquids (perfluoropolyether, PFPE), gas-phase AlF products are clearly detectable by LIF on the AlF A–X band. Quantitative AlF yields were compared for a small representative set of a widely studied family of ionic liquids based on the common 1-alkyl-3-methylimidazolium ([C(n)mim](+)) cation. Yields of (1.9 ± 0.2):1 were found from [C(2)mim][Tf(2)N] and [C(8)mim][Tf(2)N], containing the common fluorinated bis(trifluoromethylsulfonyl)imide anion ([Tf(2)N](−)). This is in quantitative agreement with previous independent low-energy ion scattering (LEIS) measurements and consistent with other independent results indicating that the longer cationic alkyl chains cover a larger fraction of the liquid surface and hence reduce anion exposure. The expected null result was obtained for the ionic liquid [C(2)mim][EtSO(4)] which contains no fluorine. These results open the way for further characterization and the potential application of this new variant of the RAS-LIF method.