Proton Transfer in a Two-Dimensional Hydrogen-Bonding Network: Water and Hydroxyl on a Pt(111) Surface

The time scale of proton transfer between H₂O and OH adsorbed on a Pt(111) surface was determined by a combination of laser-induced thermal desorption (LITD) and microscale x-ray photoelectron spectroscopy (micro-XPS). The patterned distribution OH+H₂O/H₂O/OH+H₂O was initially prepared on the Pt(111) surface by the LITD method and the time evolution of the spatial distribution of H₂O and OH was observed by the micro-XPS technique. From quantitative analyses based on a diffusion equation, we found two proton-transfer pathways with different time scales of 5.2±0.9 ns and 48±12 ns at 140 K, which were attributed to direct proton transfer to the neighbor site and H₃O⁺-mediated transfer to the next-nearest site, respectively.