Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P37: Focus Session: Structure and Dynamics of Interfacial Water I |
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Sponsoring Units: DCP Chair: Hrvoje Petek, University of Pittsburgh Room: 409 |
Wednesday, March 18, 2009 8:00AM - 8:36AM |
P37.00001: Electron Solvation Dynamics at D$_{2}$O Ice and Na/D$_{2}$O/Metal Interfaces Invited Speaker: Electron transfer (ET) across interfaces is of vital importance in different areas of physics, chemistry and biology. Using time-resolved two-photon-photoemission spectroscopy we have studied the ultrafast dynamics of interfacial ET and solvation processes in amorphous and crystalline D$_{2}$O layers on single crystal metal substrates and the influence of coadsorbed Na ions. In these experiments, photoinjection of electrons from the metal into the adsorbate conduction band is followed by ultrafast localization and solvation of the excess electrons. The subsequent energetic stabilization of these solvated electrons due to nuclear rearrangements of the polar molecular environment is accompanied by an increasing degree of localization. The observed ET rates strongly depend on the local structure of the ice. In crystalline D$_{2}$O layers we monitor the stabilization of trapped electrons at the ice vacuum interface continuously from femtoseconds up to minutes. This behavior observed for crystalline ice is fundamentally different from amorphous D$_{2}$O layers where the excess electrons have a much lower survival probability, which lifetimes of the order of 100 fs, which extend to several 10 ps if Na ions are coadsorbed at the ice surface. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 9:12AM |
P37.00002: Electron dynamics and intermolecular energy transfer in aqueous solutions studied by X-ray electron spectroscopy Invited Speaker: X-ray photoelectron spectroscopy measurements from a vacuum liquid microjet are performed to investigate the electronic structure of aqueous solutions. Here, focus is on the excited-state dynamics of chloride and hydroxide anions in water, following core-level excitation. A series of Cl$^{-}$(aq) charge-transfer-to-solvent (CTTS) states, and their ultrafast relaxation, on the time scale of the core hole, is identified from the occurrence of spectator Auger decay. Resonant oxygen 1s excitation of aqueous hydroxide, in contrast, leads to non-local decay, involving energy transfer into a neighboring water molecule. This channel is argued to arise from the weak hydrogen donor bond of OH$^{-}$(aq), and thus identifies a special transient hydration configuration, which can explain hydroxide's unusual and fast transport in water. Analogous measurements from pure water point to a similar relaxation channel, which is concluded from a strong isotope effect. The characteristic resonance spectral features are considerably stronger for H$_{2}$O(aq) than for D$_{2}$O(aq). As for OH$^{-}$(aq) the results can be understood in terms of energy transfer from the excited water molecule to a neighbor water molecule. [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:48AM |
P37.00003: Electrons tunneling through fluctuating water and proteins Invited Speaker: We have analyzed the characteristics of electron tunneling through thermally-fluctuating water and protein media [1]. A metric is defined that indicates when the tunneling propagation is well described by the average donor-acceptor tunneling interaction, as opposed to being dominated by medium fluctuations. Indeed, there is a transition distance that establishes a change in mechanism, and this distance is different for water-mediated compared to protein-mediated tunneling. Even in the fluctuation-dominated regime, we find that the three-dimensional protein fold controls the tunneling interactions. We also find that pairs of proteins in near contact may establish particularly strong water-mediated tunneling routes [2]. \\[4pt] [1] I.A. Balabin, D.N. Beratan, and S.S. Skourtis, Phys. Rev. Lett., 101, 158102 (2008). \\[0pt] [2] J. Lin, I.A. Balabin, and D.N. Beratan, Science, 310, 1311-1313 (2005). [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P37.00004: Ultraviolet Induced Disordering of the Rutile TiO2 (110) Surface Daniel Hennessy, Michael Pierce, Kee-Chul Chang, Satoru Takakusagi, Kohei Uosaki, Hoydoo You We present x-ray crystal truncation rod (CTR) data collected on the water/rutile TiO2 (110) surface before and after ultraviolet illumination. It is known that UV illumination transforms the surface superhydrophilic, with contact angle 0 degrees. [1] The wet, slightly hydrophilic surface of the clean, prepared samples exhibits a laterally ordered water adlayer that disorders under UV illumination. Contact angle measurements (CAM) show the surface exposed to ambient air is slightly hydrophobic, with contact angle 61(5) degrees. The well-protected dry surface is slightly hydrophilic, with contact angle 32(5) degrees. We propose a model based on domain growth of hydrophilic phases with laterally disordered water adatoms, consistent with some previous studies. [2] [1] R. Wang et al, Nature, 388, 431 (1997). [2] K. Hashimoto, H. Irie, and A. Fujishima, Jap J Appl Phys, 44, 8269 (2005). [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P37.00005: X-ray studies of the Density Depletion at Hydrophobic Water-Solid Interfaces Markus Mezger, Harald Reichert, Heiko Schroder, John Okasinski, Roland Roth, Helmut Dosch, Sebastian Schoder, Veijo Honkimaki, John Ralston Deeply buried hydrophobic solid-water interfaces were probed with high-energy x-ray reflectivity. The experimental data provide clear evidence for a thin density depletion with an integrated deficit corresponding to approximately 40\% of a water monolayer extending over a maximum of two molecular layers. In addition, measurements on the influence of gases (Ar, Xe, Kr, N$_2$, O$_2$, CO, CO$_2$) dissolved in the water have been performed. No effect on the hydrophobic water gap was found. The presence of nanobubbles at the interface could also be excluded. By comparing the experimental results with an generic DFT model we can give a quantitative estimation for different contributions to the observed gap size. \newline [1] M. Mezger {\em et al.}, {\em Proc. Natl. Acad. Sci. USA} {$\mathbf{103}$}, 18401 (2006). \newline [2] M. Mezger {\em et al.}, {\em J. Chem. Phys.} {$\mathbf{128}$}, 244705 (2008). [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P37.00006: First-principles study of water on Cu (110) surface Jun Ren, Sheng Meng The persistent demand for cheaper and high efficient catalysts in industrial chemical synthesis, such as ammonia, and in novel energy applications, hydrogen generation and purification in fuel cells motivated us to study the fundamental interaction involved in water-Cu system, with an intension to examine Cu as a possible competitive candidate for cheaper catalysts. Water structure and dissociation kinetics on a model open metal surface: Cu (110), have been investigated in detail based on first-principles electronic structure calculations. We revealed that in both monomer and overlayer forms, water adsorbs molecularly, with a high tendency for diffusion and/or desorption rather than dissociation on clean surfaces at low temperature. With the increase of the water coverage on the Cu (110) surface, the H-bond pattern lowers the dissociation barrier efficiently. More importantly, if the water molecule is dissociated, the hydrogen atoms can diffuse freely along the [110] direction, which is very useful in the hydrogen collection. In addition, we extended to study water on other noble metal (110) surfaces. The result confirms that Cu (110) is the borderline between intact and dissociative adsorption, differing in energy by only 0.08 eV. This may lead to promising applications in hydrogen generation and fuel cells. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P37.00007: A self-consistent polarizable electron water potential: applications to clusters and bulk Leif Jacobson We have recently re-parameterized the electron--water potential due to Turi and Borgis [J.~Chem.\ Phys.\textbf{117}, 6186 (2002)] to be used with the polarizable water potential AMOEBA for use in hydrated electron simulations. In our model the single electronic wave function polarizes the water molecules and vice versa in a fully self-consistent manner. Comparison to binding energies and relative energetics of $(\mbox{H}_2\mbox{O})_n^-$ isomers (with $n<33$) to $ab\ intio$ results show a significant increase in accuracy over the previous parameterization which used a fixed charge water model. The relative importance of polarization in various binding motifs as well as cluster and bulk molecular dynamics simulations will be presented. The simulated optical absorption spectra will also be discussed. [Preview Abstract] |
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