AVS 57th International Symposium & Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuA

Paper SS-TuA10
Dynamical Heterogeneity in Surface Reactions

Tuesday, October 19, 2010, 5:00 pm, Room Picuris

Session: Chemical Dynamics at Surfaces
Presenter: A. Utz, Tufts University
Authors: A. Utz, Tufts University
D.R. Killelea, Tufts University
V. Campbell, Tufts University
N. Chen, Tufts University
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The rates and pathways of energy flow within the reagent-surface complex play central roles in determining whether or not a given molecule will react during its encounter with the surface. State-resolved experimental studies, in combination with dynamical calculations, are beginning to paint a detailed picture of these energy flow dynamics, particularly for the model system of methane’s dissociative chemisorption on low-index Ni surfaces. Four key features of the reaction dynamics have emerged. First, the barrier to reaction can depend very sensitively on bond lengths and bond angles in the reaction complex; second, vibrational motions and their phase can modulate transition state access and the resulting energy threshold for reaction; third, such motion can be slow relative to the duration of the reagent-surface encounter; and fourth, the extent of vibrational energy flow and redistribution within the reaction complex can range from very limited to significant depending on the details for the reactive system.

We will present a conceptual framework for understanding and predicting general energy flow propensities for surface reactions. State-resolved experimental measurements, including prior examples of mode- and bond-selective surface chemistry and very recent results that explore the generality of these results for a broader range of chemical systems, will illustrate these principles. We will also include data that clearly show the ability of surface phonon excitation to modulate the energy threshold for reaction and that support recent theoretical predictions.The data point to a significant role for surface atom displacement in promoting methane activation under thermal conditions. Taken together, these studies show that the dynamical vibrational motion of reagent and substrate and the relative phase of these motions for a particular encounter can modulate the energy threshold for reaction and introduce significant energetic heterogeneity at the single molecule level.