Mass Transport in Surface Diffusion of van der Waals Bonded Systems: Boosted by Rotations?
Mass Transport in Surface Diffusion of van der Waals Bonded Systems: Boosted by Rotations?
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DOI：
10.1021/acs.jpclett.6b02024
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发表时间：
2016-12-01
影响因子：
5.7
通讯作者：
Ellis, John
中科院分区：
文献类型：
--
作者：
Hedgeland, Holly;Sacchi, Marco;Ellis, John
表面的质量输运是多相催化的关键因素。速率由跨越平动势垒的激发决定，并取决于能量格局和与表面热浴的耦合。本文采用氦自旋回波光谱法，在低覆盖（θ近似于0.07 ML）下，跟踪了苯吸附在Cu（001）上的微观运动。具体地说，我们结合实验和计算数据确定了分子运动的绝对速率和机制。观察到的速率比传统的点粒子模型高3.0 +/- 0.1倍，并且只能通过包含额外的分子（旋转）坐标来理解。我们认为，这种效应可以被描述为熵的贡献，增加了过渡态分子的数量。该过程通常与分子系统相关，并说明了在表面动力学研究中，指前因子和激活势垒的重要性。
Mass transport at a surface is a key factor in heterogeneous catalysis. The rate is determined by excitation across a translational barrier and depends on the energy landscape and the coupling to the thermal bath of the surface. Here we use helium spin echo spectroscopy to track the microscopic motion of benzene adsorbed on Cu(001) at low coverage (theta similar to 0.07 ML). Specifically, our combined experimental and computational data determine both the absolute rate and mechanism of the molecular motion. The observed rate is significantly higher by a factor of 3.0 +/- 0.1 than is possible in a conventional, point-particle model and can be understood only by including additional molecular (rotational) coordinates. We argue that the effect can be described as an entropic contribution that enhances the population of molecules in the transition state. The process is generally relevant to molecular systems and illustrates the importance of the pre-exponential factor alongside the activation barrier in studies of surface kinetics.