AVS 60th International Symposium and Exhibition
    Surface Science Thursday Sessions
       Session SS2-ThA

Paper SS2-ThA1
Angle-Resolved Dissociative Sticking Coefficients of Light Alkanes on Pt(111) Measured with Effusive Molecular Beams

Thursday, October 31, 2013, 2:00 pm, Room 202 A

Session: Surface Dynamics and Non-adiabatic Processes
Presenter: J.K. Navin, University of Virginia
Authors: J.K. Navin, University of Virginia
S.B. Donald, University of Virginia
I.A. Harrison, University of Virginia
Correspondent: Click to Email
Angle-resolved dissociative sticking coefficients (DSCs) were measured for a series of small alkanes on Pt(111) using effusive molecular beams. Measurements relevant to both thermal equilibrium (Tg = Ts) and non-equilibrium (Tg ≠ Ts) conditions were obtained. A precursor mediated microcanonical trapping (PMMT) model was useful in analyzing and comparing different kinds of experiments. The thermal DSC for methane dissociative chemisorption on Pt(111) at 700 K varied sharply around the direction of the surface normal as S(700 K, φ) = 8.2 x 10-5 cos14.5(φ). Successful modeling of this methane DSC behavior, consistent with existent supersonic molecular beam experiments involving rotationally cold molecules, required that translation parallel to the surface and rotations be treated as a spectator degree of freedoms and that the vibrational efficacy relative to normal translational energy be ηv=0.4. Across the series of alkanes, methane, ethane, and propane, the angular distributions of the thermal DSCs broadened significantly. The only angle-dependent energy that promotes thermal dissociative chemisorption of alkanes is molecular normal translational energy, En = Et cos2(φ), which should become less important as the vibrational energy of the impinging molecules increases with increasing molecular size. The bounds that the thermal angle-resolved DSCs place on theoretical models of alkane reactivity will be discussed.