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

TY - JOUR

T1 - Superthermal Al Atoms as a Reactive-Atom Probe of Fluorinated Surfaces

AU - Lane, Paul D.

AU - Gstir, Thomas

AU - Purcell, Simon M.

AU - Swierczewski, Michal

AU - Elstone, Naomi S.

AU - Bruce, Duncan W.

AU - Slattery, John M.

AU - Costen, Matthew L.

AU - McKendrick, Kenneth G.

N1 - Funding Information: We acknowledge funding from UK EPSRC (Grants EP/T03114X/1, EP/T031174/1, EP/P001459/1, and EP/T021675/1). TG was supported by the Austrian Science Fund (FWF) through the Doctoral Programme Atoms, Light, and Molecules, Project No. W1259-N27. Funding Information: Open Access is funded by the Austrian Science Fund (FWF). Publisher Copyright: © 2023 The Authors. Published by American Chemical Society

PY - 2023/7/6

Y1 - 2023/7/6

N2 - 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.

AB - 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.

UR - http://www.scopus.com/inward/record.url?scp=85164236079&partnerID=8YFLogxK

U2 - 10.1021/acs.jpca.3c02167

DO - 10.1021/acs.jpca.3c02167

M3 - Article

C2 - 37352233

AN - SCOPUS:85164236079

SN - 1089-5639

VL - 127

SP - 5580

EP - 5590

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

IS - 26

ER -