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Surface structure of thin ice Ih films
Stockholm University, Faculty of Science, Department of Physics.
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2004 (English)In: Chemical Physics Letters, ISSN 0009-2614, Vol. 395, no 1-3, 161-165 p.Article in journal (Refereed) Published
Abstract [en]

An angular dependent X-ray absorption spectroscopy study of the surface of thin ice films grown on Pt(1 1 1) is presented. Using different probing depths together with spectral calculations based on density functional theory, the spectra are interpreted in terms of the structure of surface, subsurface and bulk regions. It is shown that the crystalline ice is terminated with a large abundance of isotropically distributed free O–H groups and a distorted subsurface.

Place, publisher, year, edition, pages
2004. Vol. 395, no 1-3, 161-165 p.
URN: urn:nbn:se:su:diva-23190DOI: 10.1016/j.cplett.2004.06.141OAI: diva2:190594
Part of urn:nbn:se:su:diva-181Available from: 2004-05-13 Created: 2004-05-13 Last updated: 2009-12-03Bibliographically approved
In thesis
1. Core Level Spectroscopy of Water and Ice
Open this publication in new window or tab >>Core Level Spectroscopy of Water and Ice
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A core level spectroscopy study of ice and water is presented in this thesis. Combining a number of experiments and spectrum calculations based on density functional theory, changes in the local valence electronic structure are shown to be sensitive to the local H-bonding configurations. Exploiting this sensitivity, we are able to approach important scientific problems for a number of aggregation states; liquid water, the water-metal interface, bulk and surface of hexagonal ice.

For the H-bonded model system hexagonal ice, we have probed the occupied valence electronic structure by x-ray emission and x-ray photoelectron spectroscopy. Stepwise inclusion of different types of interactions within density functional theory, together with a local valence electron population analysis, show that it is essential to include intermolecular charge transfer together with internal s-p rehybridizations in order to describe the changes in electronic structure seen in the experiment. The attractive electrostatic interaction between water molecules is enhanced by a decrease in Pauli repulsion. A simple electrostatic model due to charge induction from the surrounding water is unable to explain the electronic structure changes.

By varying the probing depth in x-ray absorption the structure of the bulk, subsurface and surface regions is probed in a thin ice film. A pronounced continuum for fully coordinated species in the bulk is in sharp contrast to the spectrum associated with a broken symmetry at the surface. In particular molecular arrangements of water with one uncoordinated OH group have unoccupied electronic states below the conduction band that are responsible for a strong anisotropic pre-edge intensity in the x-ray absorption spectrum. The topmost layer is dominated by an almost isotropic distribution of these species, which is inconsistent with an unrelaxed surface structure.

For liquid water the x-ray absorption spectrum resembles that of the ice surface, indicating a domination of species with broken hydrogen bond configurations. The sensitivity to the local hydrogen bond configuration, in particular the sensitivity to broken bonds on the donor side, allows for a detailed analysis of the liquid water spectrum. Most molecules in liquid water are found in two-hydrogen-bonded configurations with one strong donor and one strong acceptor hydrogen bond. The results, consistent with diffraction data, imply that most molecules are arranged in strongly H-bonded chains or rings embedded in a disordered cluster network. Molecular dynamics simulations are unable to describe the experimental data.

The water overlayer on the close-packed platinum surface is studied using a combination of core-level spectroscopy and density functional theory. A new structure for water adsorption on close-packed transition metal surfaces is found, where a weakly corrugated non-dissociated overlayer interacts via alternating oxygen-metal and hydrogen-metal bonds. The latter results from a balance between metal-hydrogen bond formation and OH bond weakening.

The ultrashort core-hole lifetime of oxygen provides a powerful probe of excited state dynamics via studies of the non-radiative or radiative decay following x-ray absorption. Electrons excited into the pre-edge state for single donor species at the ice surface remain localized long enough for early time solvation dynamics to occur and these species are suggested as strong pre-existing traps to the hydrated electron. Fully coordinated molecules in the bulk contribute to a strong conduction band with electron transfer times below 0.5 femtoseconds. Upon core-ionization, both protons are found to migrate substantial distances on a femtosecond timescale. This unusually fast proton dynamics for non-resonant excitation is captured both by theory and experiment with a measurable isotope effect.

Place, publisher, year, edition, pages
Stockholm: Fysikum, 2004. 86 p.
x-ray adsorption spectroscopy, photoemission spectroscopy, x-ray photoelectron spectroscopy, platinum, x-ray emission spectroscopy, density functional theory, hydrogen-bonded, H-bond, water, ice, electronic structure, excited state dynamics, proton dynamics, water adsorption, liquid water
National Category
Physical Sciences
urn:nbn:se:su:diva-181 (URN)91-7265-911-4 (ISBN)
Public defence
2004-06-02, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Available from: 2004-05-13 Created: 2004-05-13 Last updated: 2010-01-07Bibliographically approved

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Odelius, M.Pettersson, L.G.M.Nilsson, A.
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