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

Paul D. Lane, Thomas Gstir, Simon M. Purcell, Michal Swierczewski, Naomi S. Elstone, Duncan W. Bruce, John M. Slattery, Matthew L. Costen, Kenneth G. McKendrick

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1 Citation (Scopus)
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Abstract

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 ([Cnmim]+)cation. Yields of (1.9 ± 0.2):1 were found from [C2mim][Tf2N]and [C8mim][Tf2N], containing the common fluorinated bis(trifluoromethylsulfonyl)imide anion ([Tf2N]). 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 [C2mim][EtSO4] 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.

Original languageEnglish
Pages (from-to)5580-5590
Number of pages11
JournalJournal of Physical Chemistry A
Volume127
Issue number26
Early online date23 Jun 2023
DOIs
Publication statusPublished - 6 Jul 2023

Keywords

  • Physical and Theoretical Chemistry

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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