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Bond Breaking, Electron Pushing and Proton Pulling: Active and Passive Roles in the Interaction between Aqueous Ions and Water as Manifested in the O 1s Auger Decay
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
MAX-lab, Lund UniVersity.
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2012 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 116, no 1, 3-8 p.Article in journal (Refereed) Published
Abstract [en]

A core-ionized H2O molecule in liquid water primarily relaxes through normal Auger decay, leading to a two-hole final state in which both valence holes are localized on the same water molecule. Electronic coupling to the environment, however, allows for alternative decays resembling Intermolecular Coulombic Decay (ICD), producing final states with one of the holes delocalized on a neighboring water molecule. Here we present an experimental study of such minority processes, which adds to our understanding of dynamic interactions of electronically excited H2O molecules with their local surrounding in liquid water and aqueous solution. We show that the solvation of metal-halide salts considerably influences these minority decay channels from the water 0 1s-1 state. By breaking water-water bonds, both the metal cations and halide anions are found to reduce the decay into water-water delocalized states, thus having a "passive" effect on the Auger spectrum. The halide anions also play an "active" role by opening a new ICD-like decay pathway into water-halide delocalized states. The importance of this contribution increases from F- to I-, which we suggest to be caused by a directional polarization of the halide anion toward the core-ionized H2O+ cation in the intermediate state of the Auger process. This increases the electronic overlap between the two centers and makes delocalized decays more probable. We furthermore show that F-, the smallest and most strongly hydrated of the halides, plays an additional role as proton puller during the core-hole lifetime, resulting in proton dynamics on the low femtosecond time scale. Our results represent a step forward toward a better understanding of how aqueous solutions, when exposed to soft X-rays, channel excess energy. This has implications for several aspects of physical and radiation chemistry, as well as biology.

Place, publisher, year, edition, pages
2012. Vol. 116, no 1, 3-8 p.
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-138743DOI: 10.1021/jp2041247ISI: 000298978100002OAI: oai:DiVA.org:uu-138743DiVA: diva2:379725
Available from: 2010-12-19 Created: 2010-12-19 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Solvent–Solute Interaction: Studied by Synchrotron Radiation Based Photo and Auger Electron Spectroscopies
Open this publication in new window or tab >>Solvent–Solute Interaction: Studied by Synchrotron Radiation Based Photo and Auger Electron Spectroscopies
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aqueous solutions were studied using photoelectron and Auger spectroscopy, based on synchrotron radiation and a liquid micro-jet setup.

By varying the photon energy in photoelectron spectra, we depth profiled an aqueous tetrabutylammonium iodide (TBAI) solution. Assuming uniform angular emission from the core levels, we found that the TBA+ ions were oriented at the surface with the hydrophobic butyl arms sticking into the liquid.

We investigated the association between ions and their neighbors in aqueous solutions by studying the electronic decay after core ionization. The (2p)−1 decay of solvated K+ and Ca2+ ions was studied. The main features in the investigated decay spectra corresponded to two-hole final states localized on the ions. The spectra also showed additional features, related to delocalized two-hole final states with vacancies on a cation and a neighboring water molecule. These two processes compete, and by comparing relative intensities and using the known rate for the localized decay, we determined the time-scale for the delocalized process for the two ions. We compared to delocalized electronic decay processes in Na+, Mg2+, and Al3+, and found that they were slower in K+ and Ca2+, due to different internal decay mechanisms of the ions, as well as external differences in the ion-solute distances and interactions.

In the O 1s Auger spectra of aqueous metal halide solutions, we observed features related to delocalized two-hole final states with vacancies on a water molecule and a neighboring solvated anion. The relative intensity of these feature indicated that the strength of the interaction between the halide ions and water correlated with ionic size.

The delocalized decay was also used to investigate contact ion pair formation in high concentrated potassium halide solutions, but no concrete evidence of contact ion pairs was observed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 73 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 796
Keyword
Interatomic Coulombic Decay, ICD, Auger electron spectroscopy, AES, X-ray photoelectron spectroscopy, XPS, Ultra-violet spectroscopy, UPS, localized, delocalized, double ionization potential, DIP, two hole, final states, Water, H2O, Potassium chloride, KCl, Calcium chloride, CaCl2, Ammonium, NH4, Core hole, clock, lifetime, solvated, ion, alkali, halide, Coster Kronig, MAX-lab, BESSY
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-138749 (URN)978-91-554-7980-0 (ISBN)
Public defence
2011-02-04, Häggsalen, Ångström laboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 726Available from: 2011-01-14 Created: 2010-12-19 Last updated: 2011-03-21Bibliographically approved
2. Aqueous Solutions as seen through an Electron Spectrometer: Surface Structure, Hydration Motifs and Ultrafast Charge Delocalization Dynamics
Open this publication in new window or tab >>Aqueous Solutions as seen through an Electron Spectrometer: Surface Structure, Hydration Motifs and Ultrafast Charge Delocalization Dynamics
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In spite of their high abundance and importance, aqueous systems are enigmatic on the microscopic scale. In order to obtain information about their geometrical and electronic structure, simple aqueous solutions have been studied experimentally by photo- and Auger electron spectroscopy using the novel liquid micro-jet technique in conjunction with synchrotron radiation. The thesis is thematically divided into three parts.

In the first part we utilize the surface sensitivity of photoelectron spectroscopy to probe the distributions of solutes near the water surface. In agreement with recent theoretical predictions we find that large polarizable anions, such as I- and ClO4-, display enhanced surface propensities compared to smaller rigid ions. Surface effects arising from ion-ion interactions at higher electrolyte concentrations and as function of pH are investigated. Studies of linear mono-carboxylic acids and benzoic acid show that the neutral molecular forms of such weak acids are better stabilized at the water surface than their respective conjugate base forms.

The second part examines what type of information core-electron spectra can yield about the chemical state and hydration structure of small organic molecules in water. We demonstrate that the method is sensitive to the protonation state of titratable functional groups and that core-level lineshapes are dependent on local water hydration configurations. Using a combination of photoelectron and X-ray absorption spectroscopy we also show that the electronic re-arrangement upon hydrolysis of aldehydes yields characteristic fingerprints in core-level spectra.

In the last part of this thesis we study ultrafast charge delocalization dynamics in aqueous solutions using resonant and off-resonant Auger spectroscopy. Intermolecular Coulombic decay (ICD) is found to occur in a number of core-excited solutions where excess energy is transferred between the solvent and the solute. The rate of ultrafast electron delocalization between hydrogen bonded water molecules upon oxygen 1s resonant core-excitation is found to decrease upon solvation of inorganic ions.

The presented work is illustrative of how core-level photoelectron spectroscopy can be valuable in the study of fundamental phenomena in aqueous solutions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2011. 118 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 828
Keyword
Water, Aqueous solutions, Ions, Molecular Hydration, Electron dynamics, Atmospheric Chemistry, Hydrolysis, Acid-Base Chemistry, Interatomic Coulombic Decay, ICD, Liquid Micro-Jet, X-ray Photoelectron Spectroscopy, XPS, Auger Electron Spectroscopy, AES, MAX-lab, BESSY
National Category
Physical Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-151435 (URN)978-91-554-8083-7 (ISBN)
Public defence
2011-06-01, Polhemssalen, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2011-05-11 Created: 2011-04-11 Last updated: 2011-07-01Bibliographically approved

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Ottosson, NiklasSvensson, SvanteBjörneholm, Olle

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