Heather Abbott-Lyon - Effusive molecular beam study of C2H6 dissociation on Pt(111)

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      Publication Details (including relevant citation   information):

      K.M. DeWitt, L. Valadez, H.L. Abbott, K.W.   Kolasinski, and I. Harrison, Journal of Physical Chemistry   B, 110,   6714 (2006).


      The dissociative sticking coefficient for C2H6 on Pt(111) has   been measured as a function of both gas temperature (Tg) and   surface temperature (Ts) using effusive molecular beam and   angle-integrated ambient gas dosing methods. A microcanonical   unimolecular rate theory (MURT) model of the reactive system is   used to extract transition state properties from the data as well   as to compare our data directly with supersonic molecular beam   and thermal equilibrium sticking measurements. We report for the   first time the threshold energy for dissociation, E0 ) 26.5 ( 3   kJ mol-1. This value is only weakly dependent on the other two   parameters of the model. A strong surface temperature dependence   in the initial sticking coefficient is observed; however, the   relatively weak dependence on gas temperature indicates some   combination of the following (i) not all molecular excitations   are contributing equally to the enhancement of sticking, (ii)   that strong entropic effects in the dissociative transition state   are leading to unusually high vibrational frequencies in the   transition state, and (iii) energy transfer from gas-phase   rovibrational modes to the surface is surprisingly efficient. In   other words, it appears that vibrational mode-specific behavior   and/or molecular rotations may play stronger roles in the   dissociative adsorption of C2H6 than they do for CH4. The MURT   with an optimized parameter set provides for a predictive   understanding of the kinetics of this C-H bond activation   reaction, that is, it allows us to predict the dissociative   sticking coefficient of C2H6 on Pt(111) for any combination of Ts   and Tg even if the two are not equal to one another.

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