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The dissociative sticking S0 for CH4, C2H6, and their deuterated analogs has been measured on Pt(110) as a function of surface temperature Ts under thermal ‘‘bulb’’ conditions at low gas pressures (Tg=300 K). Large increases in S0 with Ts are observed for all species, in partial qualitative agreement with previous measurements. S0 for CH4 has also been measured at a high Ar background pressure (Tg≊Ts) and shows a much faster increase with Ts than the low pressure case. This is interpreted as evidence that the dissociation mechanism for CH4 under these bulb conditions is direct rather than precursor mediated, a conclusion which is in conflict with previous interpretations. In addition, the increase in S0 with Ts for C2H6 and C2D6 exhibits concave curvature at low Ts, i.e., is non‐Arrhenius, and this is difficult to reconcile with standard precursor models. Both experimental results, however, are shown to be in qualitative accord with a previously developed dynamical model for direct dissociation, as long a... |
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