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Interaction between liquid water and hydroxide revealed by core-hole de-excitation
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2008 (English)In: Nature, ISSN 0028-0836, Vol. 455, no 7209, 89-91 p.Article in journal (Refereed) Published
Abstract [en]

The hydroxide ion plays an important role in many chemical and biochemical processes in aqueous solution(1). But ourmolecular- level understanding of its unusual and fast transport in water, and of the solvation patterns that allow fast transport, is far from complete. One proposal seeks to explain the properties and behaviour of the hydroxide ion by essentially regarding it as a water molecule that is missing a proton(2), and by inferring transport mechanisms and hydration structures from those of the excess proton. A competing proposal invokes instead unique and interchanging hydroxide hydration complexes, particularly the hypercoordinated OH-(H2O)(4) species and tri- coordinated OH-(H2O)(3) that can form a transient hydrogen bond between the H atom of the OH- and a neighbouring water molecule(3-5). Here we report measurements of core- level photoelectron emission and intermolecular Coulombic decay(6-8) for an aqueous hydroxide solution, which show that the hydrated hydroxide ion is capable of transiently donating a hydrogen bond to surrounding watermolecules. In agreement with recent experimental studies of hydroxide solutions(9-12), our finding thus supports the notion that the hydration structure of the hydroxide ion cannot be inferred from that of the hydrated excess proton.

Place, publisher, year, edition, pages
2008. Vol. 455, no 7209, 89-91 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-109093DOI: 10.1038/nature07252ISI: 000258890200042OAI: oai:DiVA.org:uu-109093DiVA: diva2:248835
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2011-07-01Bibliographically approved
In thesis
1. 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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