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Core Level Spectroscopy of Water and Ice
Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
2004 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Stockholm: Fysikum , 2004. , s. 86
Nyckelord [en]
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
Nationell ämneskategori
Fysik
Identifikatorer
URN: urn:nbn:se:su:diva-181ISBN: 91-7265-911-4 (tryckt)OAI: oai:DiVA.org:su-181DiVA, id: diva2:190599
Disputation
2004-06-02, sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2004-05-13 Skapad: 2004-05-13 Senast uppdaterad: 2010-01-07Bibliografiskt granskad
Delarbeten
1. The Hydrogen Bond in Ice Probed by Soft X-ray Spectroscopy and Density Functional Theory
Öppna denna publikation i ny flik eller fönster >>The Hydrogen Bond in Ice Probed by Soft X-ray Spectroscopy and Density Functional Theory
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2005 (Engelska)Ingår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, ISSN 0021-9606, Vol. 122, nr 15, s. 154505-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We combine photoelectron and x-ray absorption spectroscopy with density functional theory to derive a molecular orbital picture of the hydrogen bond in ice. We find that the hydrogen bond involves donation and back-donation of charge between the oxygen lone pair and the O–H antibonding orbitals on neighboring molecules. Together with internal s-p rehybridization this minimizes the repulsive charge overlap of the connecting oxygen and hydrogen atoms, which is essential for a strong attractive electrostatic interaction. Our joint experimental and theoretical results demonstrate that an electrostatic model based on only charge induction from the surrounding medium fails to properly describe the internal charge redistributions upon hydrogen bonding.

Ort, förlag, år, upplaga, sidor
American Institute of Physics, 2005
Nyckelord
ice, hydrogen bonds, X-ray absorption spectra, density functional theory, photoelectron spectra, molecular electronic states, oxygen compounds
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-23189 (URN)10.1063/1.1879752 (DOI)
Anmärkning
Part of urn:nbn:se:su:diva-286Tillgänglig från: 2004-05-13 Skapad: 2004-05-13 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
2. Surface structure of thin ice Ih films
Öppna denna publikation i ny flik eller fönster >>Surface structure of thin ice Ih films
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2004 (Engelska)Ingår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 395, nr 1-3, s. 161-165Artikel i tidskrift (Refereegranskat) 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.

Identifikatorer
urn:nbn:se:su:diva-23190 (URN)10.1016/j.cplett.2004.06.141 (DOI)
Anmärkning
Part of urn:nbn:se:su:diva-181Tillgänglig från: 2004-05-13 Skapad: 2004-05-13 Senast uppdaterad: 2017-12-13Bibliografiskt granskad
3. Structure of the first coordination shell in liquid water
Öppna denna publikation i ny flik eller fönster >>Structure of the first coordination shell in liquid water
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2004 (Engelska)Ingår i: Science, ISSN 1095-9203, Vol. 304, nr 5673, s. 995-999Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

X-ray absorption spectroscopy and x-ray Raman scattering were used to probe the molecular arrangement in the first coordination shell of liquid water. The local structure is characterized by comparison with bulk and surface of ordinary hexagonal ice Ih and with calculated spectra. Most molecules in liquid water are in two hydrogen–bonded configurations with one strong donor and one strong acceptor hydrogen bond in contrast to the four hydrogen–bonded tetrahedral structure in ice. Upon heating from 25°C to 90°C, 5 to 10% of the molecules change from tetrahedral environments to two hydrogen–bonded configurations. Our findings are consistent with neutron and x-ray diffraction data, and combining the results sets a strong limit for possible local structure distributions in liquid water. Serious discrepancies with structures based on current molecular dynamics simulations are observed

Ort, förlag, år, upplaga, sidor
Science, 2004
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-23191 (URN)10.1126/science.1096205 (DOI)
Anmärkning
Part of urn:nbn:se:su:diva-181Tillgänglig från: 2004-05-13 Skapad: 2004-05-13 Senast uppdaterad: 2009-12-30Bibliografiskt granskad
4. Structure and Bonding of Water on Pt(111)
Öppna denna publikation i ny flik eller fönster >>Structure and Bonding of Water on Pt(111)
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2002 (Engelska)Ingår i: Physical Review Letters, ISSN 1079-7114, Vol. 89, nr 27, s. 276102-276105Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We address the adsorption of water on Pt(111) using x-ray absorption, x-ray emission, and x-ray photoelectron spectroscopy along with calculations in the framework of density functional theory. Using the direct relationship between the electronic structure and adsorbate geometry, we show that in the first layer all the molecules bind directly to the surface and to each other through the in-layer H bonds without dissociation, creating a nearly flat overlayer. The water molecules are adsorbed through alternating metal-oxygen (M-O) and metal-hydrogen (M-HO) bonds.

Ort, förlag, år, upplaga, sidor
American Physical Society, 2002
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-23192 (URN)10.1103/PhysRevLett.89.276102 (DOI)
Anmärkning
Part of urn:nbn:se:su:diva-181Tillgänglig från: 2004-05-13 Skapad: 2004-05-13 Senast uppdaterad: 2009-12-30Bibliografiskt granskad
5. Ultrafast Molecular Dissociation of Water in Ice
Öppna denna publikation i ny flik eller fönster >>Ultrafast Molecular Dissociation of Water in Ice
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2004 (Engelska)Ingår i: Physical Review Letters, ISSN 1079-7114, Vol. 93, s. 148302-148305Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Using x-ray emission and photoemission spectroscopies to measure the occupied valence levels in a thin crystalline ice film, we resolve the ionization-induced dissociation of water in ice on a femtosecond time scale. Isotope substitution confirms proton transfer during the core-hole lifetime in spite of the nonresonant excitation. Through ab initio molecular dynamics on the core-ionized state, the dissociation and spectrum evolution are followed at femtosecond intervals. The theoretical simulations confirm the experimental analysis and allow for a detailed study of the dissociative reaction path.

Ort, förlag, år, upplaga, sidor
The American Physical Society, 2004
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-23193 (URN)10.1103/PhysRevLett.93.148302 (DOI)
Anmärkning
Part of urn:nbn:se:su:diva-181Tillgänglig från: 2004-05-13 Skapad: 2004-05-13 Senast uppdaterad: 2009-12-30Bibliografiskt granskad
6. Probing the Electron Delocalization in Liquid Water and Ice at Attosecond Time Scales
Öppna denna publikation i ny flik eller fönster >>Probing the Electron Delocalization in Liquid Water and Ice at Attosecond Time Scales
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2007 (Engelska)Ingår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, ISSN 0031-9007, Vol. 99, nr 21, s. 217406-Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We determine electron delocalization rates in liquid water and ice using core-hole decay spectroscopy. The hydrogen-bonded network delocalizes the electrons in less than 500 as. Broken or weak hydrogen bonds-in the liquid or at the surface of ice-provide states where the electron remains localized longer than 20 fs. These asymmetrically bonded water species provide electron traps, acting as a strong precursor channel to the hydrated electron

Ort, förlag, år, upplaga, sidor
American Physical Society, 2007
Nationell ämneskategori
Fysik
Identifikatorer
urn:nbn:se:su:diva-23194 (URN)10.1103/PhysRevLett.99.217406 (DOI)
Anmärkning
Part of urn:nbn:se:su:diva-181. Tillgänglig från: 2004-05-13 Skapad: 2004-05-13 Senast uppdaterad: 2017-12-13Bibliografiskt granskad

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