Extremely fast water dimer diffusion on Pd111

1
Extremely fast water dimer diffusion on Pd(111)

• Science, 297, 1850 (2002) Mitsui, Rose, Fomin,
  Ogletree and Salmeron
• report, among other interesting observations, the
  extremely fast water dimer
• diffusion on Pd(111) (about 10000 faster compared
  with water monomers).
• A theoretical model based on nearly-free
  rotation of dimers and
• H-bond-acceptor monomer exchange provides a
  semi-quantitative
• explanation for the experimental observation
  (Ranea, Michaelides,
• Ramirez, de Andres, Verges and King Phys. Rev.
  Lett., in press).

2
The waltz of the water dimers
Dimer diff. barrier over bridge site 0.26 eV
20 meV rotation barrier
Barrier 0.11 eV
kT
Wagging mode 100 cm-1
Tunneling through the central barrier makes dimer
diffusion faster compared with the monomer one.
Barrier 0.11 eV (0.025 eV in gas phase)
kT
V.A. Ranea, A. Michaelides, R. Ramirez, P.L. de
Andres, J.A. Verges and D.A. King. PRL (in
press).