Solving Water Dimers’ Surface Structure

Water’s behavior on metal surfaces lies at the core of much of electrochemistry and surface catalysis. Yet key questions regarding that behavior remain the subject of debate. Some of those questions—including ones about the structure and orientation of water clusters—have now been answered by a study combining scanning tunneling microscopy and quantum computations. By using an STM tip to nudge isolated water molecules on a platinum surface, Maki Kawai of the University of Tokyo; Líney Árnadóttir of Oregon State University, Corvallis; and coworkers formed isolated hydrogen-bonded water dimers. Then the team used an STM-based method to measure vibrational spectra of individual dimers and determine their orientations (ACS Nano 2014, DOI: 10.1021/nn504824z). They find that one of the monomers bonds to the surface through oxygen. Its mate forms a hydrogen bond by sidling next to the surface-bound species with its OH group perpendicular to the surface. Those findings, which contradict older theoretical studies, can help improve surface chemistry modeling methods, which are used for interpreting experimental measurements and predicting surface phenomena.