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arXiv 1404.7263physics.chem-phcond-mat.mtrl-sci
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氢在Ru(0001)上扩散的量子效应

Quantum effects in the diffusion of hydrogen on Ru(0001)

Eliza M. McIntosh, K. Thor Wikfeldt, John Ellis, Angelos Michaelides, William Allison

摘要:

理解氢在金属表面上的扩散是很重要的,不仅因为它在多相催化和氢燃料电池技术中的作用,而且因为它提供了模型系统,可以在明确定义的条件下研究隧道效应。在这里,我们报告的氦自旋回波测量的原子尺度运动的氢在Ru(0001)表面在75和250 K之间。量子效应是明显的,在温度高达200 K,而低于120 K,我们观察到一个隧道主导的温度无关的跳跃率为1.9 $\times$ 10 $^9$ s $^{-1}$,许多数量级比以前看到的更快。量子过渡态理论计算的基础上从头算路径积分模拟再现的温度依赖性的速率在较高的温度和预测的交叉隧道主导的扩散在低温下,虽然隧道速率被低估,突出了未来的实验和理论研究的需要氢扩散定义明确的表面。

英文摘要:

An understanding of hydrogen diffusion on metal surfaces is important, not just for its role in heterogeneous catalysis and hydrogen fuel cell technology, but also because it provides model systems where tunneling can be studied under well-defined conditions. Here we report helium spin-echo measurements of the atomic-scale motion of hydrogen on the Ru(0001) surface between 75 and 250 K. Quantum effects are evident at temperatures as high as 200 K, while below 120 K we observe a tunneling-dominated temperature independent jump rate of 1.9$\times$10$^9$ s$^{-1}$, many orders of magnitude faster than previously seen. Quantum transition state theory calculations based on ab initio path-integral simulations reproduce the temperature dependence of the rate at higher temperatures and predict a crossover to tunneling-dominated diffusion at low temperatures, although the tunneling rate is under-estimated, highlighting the need for future experimental and theoretical studies of hydrogen diffusion on well-defined surfaces.

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