Reaction of a Laser-Ablated Al Plume with a Fluorinated Ionic-Liquid Surface: Characterizing the AlF-Producing...

The species present in a laser-ablated Al plume have been characterized and their reactivity with the surface of the ionic liquid, 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)-imide ([C₂mim]-[Tf₂N]), has been investigated. Al atoms were confirmed to be present and their kinetic-energy distributions determined by laser-induced fluorescence time-of-flight measurements, over a wider range of ablation fluences than reported previously. Cations were detected directly using an in-line microchannel-plate-detector assembly. Corroboratory measurements of the ions entrained in a He buffer gas confirmed Al⁺ to be the only cation present in measurable concentrations. The Al⁺ kinetic energies were determined by time-of-flight and found to be much hotter than anticipated based on previous independent reports; under the highest-fluence conditions examined (30 mJ pulse^-1, nominal fluence of 42 J cm^-2), the mean kinetic energies of Al and Al⁺ were 17 and 450 eV, respectively. Using an electrostatic deflector, it was shown that both Al and Al⁺ projectiles produce AlF through reaction at the surface of the ionic liquid [C₂mim]-[Tf₂N] containing a fluorinated anion. The AlF yield from Al⁺ is mildly dominant under our conditions. AlF leaves the surface with near-thermal kinetic energy and rotational distributions. There is a minor component of vibrationally excited AlF which is confined to the fastest products. The observation of near-complete thermalization of the AlF products is consistent with significant penetration of the projectiles into the liquid, as would be anticipated from the high incident kinetic energies, particularly for Al⁺. The results provide new insights into reactive-atom scattering (RAS) from fluorine-containing liquid surfaces.