Inelastic and Reactive Scattering Dynamics of Hyperthermal Oxygen Atoms on Ionic Liquid Surfaces: [emim][NTf{sub 2}] and [C{sub 12}mim][NTf{sub 2}]

Journal Article · Fri May 20 00:00:00 EDT 2011 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.3562700· OSTI ID:21511589

Bohan, Wu; Jianming, Zhang; Minton, Timothy K ^[1]; McKendrick, Kenneth G ^[2]; Slattery, John M ^[3]; Yockel, Scott; Schatz, George C ^[4]

---

1. Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717 (United States)
2. School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom)
3. Department of Chemistry, University of York, Heslington, York YO10 5DD (United Kingdom)
4. Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113 (United States)

Collisions of hyperthermal oxygen atoms, with an average translational energy of 520 kJ mol{sup -1}, on continuously refreshed ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([emim][NTf{sub 2}]) and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C{sub 12}mim][NTf{sub 2}]), 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 H{sub 2}O 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{sub 12}mim][NTf{sub 2}], is substantially more reactive than the liquid with the shorter alkyl chain, [emim][NTf{sub 2}], 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 (C{sub 30}H{sub 62}). 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][NTf{sub 2}] than for [C{sub 12}mim][NTf{sub 2}].

• OSTI ID: 21511589
• Journal Information: AIP Conference Proceedings, Vol. 1333, Issue 1; Conference: 27. international symposium on rarefied gas dynamics, Pacific Grove, CA (United States), 10-15 Jul 2010; Other Information: DOI: 10.1063/1.3562700; (c) 2011 American Institute of Physics; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
ANGULAR DISTRIBUTION
ATOM COLLISIONS
ATOMS
CHEMICAL REACTIONS
COMPARATIVE EVALUATIONS
HYDROGEN
INCIDENCE ANGLE
INELASTIC SCATTERING
LIQUIDS
MASS SPECTROMETERS
MOLECULAR DYNAMICS METHOD
MOLTEN SALTS
OXYGEN
REACTIVITY
SQUALANE
STOICHIOMETRY
SURFACES
TIME-OF-FLIGHT METHOD
WATER
ALKANES
CALCULATION METHODS
COLLISIONS
DISTRIBUTION
ELEMENTS
EVALUATION
FLUIDS
HYDROCARBONS
HYDROGEN COMPOUNDS
MEASURING INSTRUMENTS
NONMETALS
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
SALTS
SCATTERING
SPECTROMETERS