<p>The structure, bonding and chemistry of water and hydroxyl on metal surfaces are presented. Synchrotron based x-ray photoelectron- and x-ray absorption spectroscopy along with density functional theory calculations mainly form the basis of the results. Conditions span the temperature range 35 - 520 K and pressures from ultra-high vacuum (~10 fAtm) to near ambient pressures (~1 mAtm). The results provide, e.g, new insights on the importance of hydrogen bonding for surface chemical kinetics.</p><p>Water adsorbs intact on the Pt(111), Ru(001) and Cu(110) surfaces at low temperatures forming 2-dimensional wetting layers where bonding to the metal (M) mainly occurs via H<sub>2</sub>O-M and M-HOH bonds. Observed isotope differences in structure and kinetics for H<sub>2</sub>O and D<sub>2</sub>O adsorption on Ru(001) are due to qualitatively different surface chemistries. D<sub>2</sub>O desorbs intact but H<sub>2</sub>O dissociates in kinetic competition with desorption similar to the D<sub>2</sub>O/Cu(110) system. The intact water layers are very sensitive to x-ray and electron induced damage.</p><p>The mixed H<sub>2</sub>O:OH phase on Ru(001) consists of stripe-like structures 4 to 6 Ru lattice parameters wide where OH decorates the edges of the stripes. On Pt(111), two different long-range ordered mixed H<sub>2</sub>O:OH structures are found to be inter-related by geometric distortions originating from the asymmetric H-bond donor-acceptor properties of OH towards H<sub>2</sub>O.</p><p>Water adsorption on Cu(110) was studied at near ambient conditions and compared to Cu(111). Whereas Cu(111) remains clean, Cu(110) holds significant amounts of water in a mixed H<sub>2</sub>O:OH layer. The difference is explained by the differing activation barriers for water dissociation, leading to the presence of OH groups on Cu(110) which lowers the desorption kinetics of water by orders of magnitude due to the formation of strong H<sub>2</sub>O-OH bonds. By lowering the activation barrier for water dissociation on Cu(111) by pre-adsorbing atomic O, generating adsorbed OH, similar results to those on Cu(110) are obtained.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:su-1246 |
| Date | January 2006 |
| Creators | Andersson, Klas |
| Publisher | Stockholm University, Department of Physics, Stockholm : Fysikum |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
Page generated in 0.0022 seconds