TY - JOUR
T1 - Scattering Dynamics of Hyperthermal Oxygen Atoms on Ionic Liquid Surfaces: [emim][NTf2] and [C(12)mim][NTf2]
AU - Wu, Bohan
AU - Zhang, Jianming
AU - Minton, Timothy K.
AU - McKendrick, Kenneth G.
AU - Slattery, John M.
AU - Yockel, Scott
AU - Schatz, George C.
PY - 2010/3/11
Y1 - 2010/3/11
N2 - Collisions of hyperthermal oxygen atoms, with all average laboratory-frame 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 it 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 call be empirically categorized as thermal and nonthermal. Nonthermal scattering is more probable for both O and OH products. The observation of OH confirms that ill least some reactive sites, presumably alkyl groups, most 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 oil the number of abstractable hydrogen atoms. Molecular dynamics models of these Surfaces shed light oil this change ill 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 oil 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 nonreactive 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)mim][NTf2].
AB - Collisions of hyperthermal oxygen atoms, with all average laboratory-frame 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 it 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 call be empirically categorized as thermal and nonthermal. Nonthermal scattering is more probable for both O and OH products. The observation of OH confirms that ill least some reactive sites, presumably alkyl groups, most 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 oil the number of abstractable hydrogen atoms. Molecular dynamics models of these Surfaces shed light oil this change ill 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 oil 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 nonreactive 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)mim][NTf2].
KW - SUM-FREQUENCY GENERATION
KW - SELF-ASSEMBLED MONOLAYERS
KW - REACTIVE SCATTERING
KW - HYDROCARBON SURFACE
KW - MOLECULAR-DYNAMICS
KW - INELASTIC-SCATTERING
KW - O(P-3) ATOMS
KW - EXCITATION-FUNCTION
KW - SQUALANE SURFACE
KW - COLLISIONS
UR - http://www.scopus.com/inward/record.url?scp=77949277891&partnerID=8YFLogxK
U2 - 10.1021/jp910641s
DO - 10.1021/jp910641s
M3 - Article
SN - 1932-7447
VL - 114
SP - 4015
EP - 4027
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 9
ER -