title: Quantum Effects in the Diffusion of Hydrogen on Ru(0001).
abstract: An understanding of hydrogen diffusion on metal surfaces is important not only 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 × 109s-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. However, the tunneling rate is underestimated, highlighting the need for future experimental and theoretical studies of hydrogen diffusion on this and other well-defined surfaces.
authors.affiliation: The Cavendish Laboratory , J. J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom.
authors.forename: Eliza M
authors.initials: EM
authors.lastname: McIntosh
authors.affiliation: Thomas Young Centre, London Centre for Nanotechnology and Department of Chemistry, University College London , London WC1E 6BT, United Kingdom ; Science Institute, VR-III, University of Iceland , 107 Reykjavik, Iceland.
authors.forename: K Thor
authors.initials: KT
authors.lastname: Wikfeldt
authors.affiliation: The Cavendish Laboratory , J. J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom.
authors.forename: John
authors.initials: J
authors.lastname: Ellis
authors.affiliation: Thomas Young Centre, London Centre for Nanotechnology and Department of Chemistry, University College London , London WC1E 6BT, United Kingdom.
authors.forename: Angelos
authors.initials: A
authors.lastname: Michaelides
authors.affiliation: The Cavendish Laboratory , J. J. Thomson Avenue, Cambridge, CB3 0HE, United Kingdom.
authors.forename: William
authors.initials: W
authors.lastname: Allison