Inelastic and Reactive Scattering Dynamics of Hyperthermal Oxygen Atoms on Ionic Liquid Surfaces: [emim][NTf2] and [C(12)mim][NTf2]

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Published copy (DOI)

Author(s)

  • Bohan Wu
  • Jianming Zhang
  • Timothy K. Minton
  • Kenneth G. McKendrick
  • John M. Slattery
  • Scott Yockel
  • George C. Schatz

Department/unit(s)

Publication details

Title of host publication27TH INTERNATIONAL SYMPOSIUM ON RAREFIED GAS DYNAMICS, 2010, PTS ONE AND TWO
DatePublished - 2011
Pages516-521
Number of pages6
PublisherAMER INST PHYSICS
Place of PublicationMELVILLE
EditorsDA Levin, IJ Wysong, AL Garcia
Volume1333
EditionPART 1
Original languageEnglish
ISBN (Print)978-0-7354-0889-0

Abstract

Collisions of hyperthermal oxygen atoms, with an average translational energy of 520 kJ mol(-1), on continuously refreshed ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([emim][NTf2]) and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C(12)mim][NTf2]), were studied with the use of a beam-surface scattering technique. Time-of-flight and angular distributions of inelastically scattered O and reactively scattered OH and H2O were collected for various angles of incidence with the use of a rotatable mass spectrometer detector. For both O and OH, two distinct scattering processes were identified, which can be empirically categorized as thermal and non-thermal. Non-thermal scattering is more probable for both O and OH products. The observation of OH confirms that at least some reactive sites, presumably alkyl groups, must be exposed at the surface. The ionic liquid with the longer alkyl chain, [C(12)mim][NTf2], is substantially more reactive than the liquid with the shorter alkyl chain, [emim][NTf2], and proportionately much more so than would be predicted simply from stoichiometry based on the number of abstractable hydrogen atoms. Molecular dynamics models of these surfaces shed light on this change in reactivity. The scattering behavior of O is distinctly different from that of OH. However, no such differences between inelastic and reactive scattering dynamics have been seen in previous work on pure hydrocarbon liquids, in particular the benchmark, partially branched hydrocarbon, squalane (C30H62). The comparison between inelastic and reactive scattering dynamics indicates that inelastic scattering from the ionic liquid surfaces takes place predominantly at non-reactive sites that are effectively stiffer than the reactive alkyl chains, with a higher proportion of collisions sampling such sites for [emim][NTf2] than for [C(12)mitn][NTf2].

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