On the basis of the results of density functional theory calculations, a novel mechanism was proposed for the diffusion of water dimers on metal surfaces. This relied upon the ability of H bonds to rearrange via quantum tunneling. The mechanism involved quasi-free rotation of the dimer, and the exchange of H-bond donor and acceptor molecules. At certain temperatures, water dimers diffused more rapidly than did water monomers; thus providing an explanation for the experimentally measured high diffusivity of water dimers on Pd.
Water Dimer Diffusion on Pd Assisted by an H-Bond Donor-Acceptor Tunneling Exchange. V.A.Ranea, A.Michaelides, R.Ramirez, P.L.de Andres, J.A.Verges, D.A.King: Physical Review Letters, 2004, 92, 136104 (4pp)