Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T37: Focus Session: Structure and Dynamics of Interfacial Water III |
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Sponsoring Units: DCP Chair: Kenneth Jordan, University of Pittsburgh Room: 409 |
Wednesday, March 18, 2009 2:30PM - 3:06PM |
T37.00001: Study of Water Adsorbed on the Cu(110) Surface using Scanning Tunneling Microscopy and Electron Stimulated Desorption Ion Angular Distribution Invited Speaker: The structure of water layer on the Cu(110) surface formed via hydrogen bonding has been investigated with scanning tunneling microscopy (STM), electron stimulated desorption ion angular distribution (ESDIAD), and density functional theory (DFT) calculations. STM results revealed 1D chain and 2D island growth at low temperature ($\sim $80 K) and at low coverage regime. ESDIAD results at low coverage indicate that there are two kinds of O-H bonds of water molecules that are pointing out of the surface plane. At higher coverage the two-dimensional islands of water prevail, eventually covering the whole surface at the saturation coverage. Dynamic changes in the structure of the water layer and the local O-H bond direction have also been investigated as a function of annealing temperature. Using DFT calculation, a model of the 1D chain structure will be presented. [Preview Abstract] |
Wednesday, March 18, 2009 3:06PM - 3:42PM |
T37.00002: Theoretical description of excited state dynamics in nanostructures Invited Speaker: There has been much progress in the synthesis and characterization of nanostructures however, there remain immense challenges in understanding their properties and interactions with external probes in order to realize their tremendous potential for applications (molecular electronics, nanoscale opto-electronic devices, light harvesting and emitting nanostructures). We will review the recent implementations of TDDFT to study the optical absorption of biological chromophores, one-dimensional polymers and layered materials. In particular we will show the effect of electron-hole attraction in those systems. Applications to the optical properties of solvated nanostructures as well as excited state dynamics in some organic molecules will be used as text cases to illustrate the performance of the approach. Work done in collaboration with A. Castro, M. Marques, X. Andrade, J.L Alonso, Pablo Echenique, L. Wirtz, A. Marini, M. Gruning, C. Rozzi, D. Varsano and E.K.U. Gross. [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 3:54PM |
T37.00003: Interfacial water in electric field Alenka Luzar, D. Bratko, C.D. Daub As accessible experimental length scales become shorter, the modification of interfacial properties of water using electric field (electrowetting) must come to grips with novel effects existing at the nanoscale. I will briefly survey some of our recent progress we have made in understanding these effects using molecular simulations. [Preview Abstract] |
Wednesday, March 18, 2009 3:54PM - 4:06PM |
T37.00004: Molecular Simulation of Reverse Micelles Janamejaya Chowdhary, Branka Ladanyi Reverse micelles (RM) are surfactant assemblies containing a nanosized water pool dissolved in a hydrophobic solvent. Understanding their properties is crucial for insight into the effect of confinement on aqueous structure, dynamics as well as physical processes associated with solutes in confinement. We perform molecular dynamics simulations for the RM formed by the surfactant Aerosol-OT (AOT) in isooctane (2,2,4-trimethyl pentane) in order to study the effect of reverse micelle size on the aqueous phase. The structure of the RM is quantified in terms of the radial and pair density distributions. Dynamics are studied in terms of the mean squared displacements and various orientational time correlation functions in different parts of the RM so as to understand the effect of proximity to the interface on aqueous dynamics. Shape fluctuations of the RM are also analyzed. [Preview Abstract] |
Wednesday, March 18, 2009 4:06PM - 4:18PM |
T37.00005: Ti-O bond distance fluctuations at the hydrated rutile (110) surface Nitin Kumar, Paul Kent, David Cole, David Wesolowski, James Kubicki, Jorge Sofo We studied water on the rutile (110) surface using ab-initio molecular dynamics simulations in NVT ensemble at 280K, 300K, and 320K. Water adsorbs on the 5-fold coordinated titanium atoms or dissociates transferring a proton to a bridging-oxygen atom. The equilibrium between these configurations is dynamical and depends on temperature and water coverage. The titanium-oxygen bond distances at the surface can change as much as 12{\%} depending on the number of hydrogen atoms bonded to oxygen. Hydrogen bonds also affect this distance. A measurement of the Ti-O distance at the surface can be used to estimate the average degree of dissociation. In view of our simulation results, the experimental evidence, such as photoelectron diffraction, indicates a low degree of dissociation under dry conditions. [Preview Abstract] |
Wednesday, March 18, 2009 4:18PM - 4:30PM |
T37.00006: Interplay between hydrogen bonding and electron solvation on hydrated TiO2 surface Jin Zhao, Kenneth Jordan, Jinlong Yang, Hrvoje Petek At metal-oxide/protic-solvent interfaces, partially hydrated or ``wet electron'' states represent the lowest energy pathway for electron transfer.$^{1}$ Through a joint two-photo photoemission (2PP) experiment and density function theory (DFT) study, we identified the electronic states corresponding to the partially solvated or wet electron state in H$_{2}$O overlayers on rutile TiO$_{2}$(110) surface. We find that a network of dangling H atoms can stabilize photoexcited electrons, in so-called wet-electron states. The energies of the ``wet electron'' states correlate closely with the number and configuration of the dangling H atoms involved in stabilizing them. We also performed DFT calculations of H$_{2}$O and H covered anatase (101) surface. Comparing with rutile (110), anatase (101) surface accommodates weaker H$_{2}$O molecule-surface hydrogen bonding. Our calculated wet electron state on anatase (101) surface has a lower energy than on rutile. Moreover, the longer distance between the adjacent adsorbate sites and the lower binding energy of H$_{2}$O allow for greater freedom for the adsorbed molecules to undergo structural relaxation in solvation of injected electrons. These differences might contribute to the higher photocatalytic activity of anatase compared with rutile. [1] K. Onda B. Li, J. Zhao, K.D. Jordan, J. Yang and H. Petek, \textit{Science} \textbf{308}, 1154 (2005). [Preview Abstract] |
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