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Funding National Science Foundation R. A. Welch Foundation Hungarian Science Foundation

Excess Electrons in W ater: Clusters, Interfaces, and the Bulk. Laszlo Turi Adam Madarasz (Eotvos Loring U., Budapest) Wen-Shyan Sheu (Fu-Jen University, Taipei) Daniel Borgis (Universite d’Evry / ENS Paris). Funding National Science Foundation R. A. Welch Foundation

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Funding National Science Foundation R. A. Welch Foundation Hungarian Science Foundation

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  1. Excess Electrons in Water: Clusters, Interfaces, and the Bulk Laszlo Turi Adam Madarasz (Eotvos Loring U., Budapest) Wen-Shyan Sheu (Fu-Jen University, Taipei) Daniel Borgis (Universite d’Evry / ENS Paris) • Funding • National Science Foundation • R. A. Welch Foundation • Hungarian Science Foundation • Eötvös Fellowship • Bolyai János Fellowship • Széchenyi Professor Fellowship

  2. J. R. R. Verlet, A. E. Bragg, A. Kammrath, O. Cheshnovsky, and D. M. Neumark, Science, 307, 93 (2005). Water Cluster Anions: distinct “isomers” Systematic variations • What are the characteristic properties which distinguish the different classes? Common sets of structural motifs? • Backing pressure/thermodynamic conditions. Non-equilibrium?

  3. Anionic clustersand hydrated electrons:localization mode/”binding motif” and structure ↔ clusters “infinite” cluster ↔

  4. The Toolkit for Mixed Quantum-ClassicalMD Simulations { quantum mechanicale- + classical solvent molecules } Components: • N classical water molecules (SPC model + internal flexibility) • the excess electron (wave function represented on dual [k,r] grid) • the electron-moleculeinteraction (pseudopotential*) • the force acting on the molecular nuclei: = classical force (from the solvent) + quantum force (from the solute) = FH2O + FQ • A sampling scheme: (adiabatic) time evolution of the system: * Turi, L.; Gaigeot, M.-P.; Levy, N.; Borgis, D.;J. Chem. Phys., 2001, 114, 7805. Turi, L.; Borgis, D.J. Chem. Phys., 2002, 117, 6186.

  5. Applicability of the Pseudopotential E0 = -3.12 eV  Es-p,max = 1.92 eV (vs. 1.72) RG = <r2>1/2 = 2.4 A  • Bulk: • VDE for n=12 clusters MP2/6-31(1+3+)G* vs. the pseudopotential Turi, L.;Madarász, Á.; Rossky, P. J.; JCP 125, 014308 (2006).

  6. Cluster Simulations: Surface states vs. internal states n = 20, 30, 45, 66, 104, 200 + 500, 1000 nominal T = 100K, 200K, 300K (s  p; n = 45. T = 200K) L. Turi, W.-S. Sheu, P. J. Rossky, Science 309, 914 (2005), ibid. 310, 1719 (2005).

  7. E0,1 300K bulk gap ~35D m 300K bulk n -1/3 0.20 Average surface state energetic behavior vs. interior states and vs. expt. old lines, new points: n = 200, 500, 1000 (surface and internal at 200K) expt. (M. Johnson + coworkers) - spectral gap (expt) internal (expt) E0 internal 0 0.1 0.2 0.3 n -1/3

  8. From: David M. Bartels - J. Chem. Phys. 115, 4404 (2001). • Simulations: surface internal internal surface Electron radius and kinetic energy

  9. Hydrated electrons at water/vacuum interfaces:the infinite cluster limit • Cases: • Ambient water surface (300 K) • Supercooled water surface (200 K) • Hexagonal ice surface (200 K) • Amorphous solid (quenched) water surface (100 K) • Starting point: charge-neutral equilibrium surfaces • Dynamic simulations of surface accommodation and final states Localization analysis Á. Madarász, P. J. Rossky, L. Turi, JCP 126, 234707 (2007).

  10. Interior and surface hydrated electrons at liquidwater/vacuum interfaces (meta)stable surface states at 200 K vs. spontaneous internal states at 300 K Dz(t) 10 ps

  11. Surface vs. Internal states

  12. Alternative surface states fully reorganized -OH partly reorganized from dangling -OH restricted reorganization ‘otherwise occupied’ -OH partly reorganized -OH

  13. 4 1 D 3 2 A (Credit: Mark Johnson) D A Donor-Acceptor characterization of water molecules 1AA 2AD 3 DD 4 AD iceAADD strong electron binding Concept: N. I. Hammer, J.-W. Shin, J. M. Headrick, E. G. Diken, J. R. Roscioli, G. H. Weddle, and M. A. Johnson, Science, 306, 675 (2004).

  14. Hydrated electrons at solid water interfaces H-bonding structure analysis: AA (solid) and AAD (dashed) Ice Ih, 200K AAD AA ASW, 100K AAD

  15. Equilibrium and non-equilibrium preparation of cluster anions • quenched clusters (QC) Prepare warm (ambient) neutral equilibrium structures → quench them gradually to a sequence of lowerT’s • Cluster surface site analysis • metastable clusters (MC) Alternative preparation protocol: assemble the neutral clusters at very low T→ warm them up gradually to the desired higher T. metastable clusters have never “seen” annealing temperatures • Add the electron and relax (for ~ 200 ps).

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