| 1. |
- Bergersen, Henrik, et al.
(författare)
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A photoelectron spectroscopic study of aqueous tetrabutylammonium iodide
- 2007
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 19:32, s. 326101-
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectron spectra of tetrabutylammonium iodide (TBAI) dissolved in water have been recorded using a novel experimental set-up, which enables photoelectron spectroscopy of volatile liquids. The set-up is described in detail. Ionization energies are reported for I− 5p, I− 4d, C 1s and N 1s. The C 1s spectrum shows evidence of inelastic scattering of the photoelectrons, that differs from the case of TBAI in formamide.
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| 2. |
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| 3. |
- Gråsjö, Johan, et al.
(författare)
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Local Electronic Structure of Functional Groups in Glycine As Anion, Zwitterion, and Cation in Aqueous Solution
- 2009
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:49, s. 16002-16006
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen and oxygen K emission spectra of glycine in the form of anions, zwitterions, and cations in aqueous solution are presented. It is shown that protonation has a dramatic influence on the local electronic structure and that the functional groups give a distinct spectral fingerprint.
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| 4. |
- Miteva, Tsveta, et al.
(författare)
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The All-Seeing Eye of Resonant Auger Electron Spectroscopy : A Study on Aqueous Solution Using Tender X-rays
- 2018
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:15, s. 4457-4462
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption and Auger electron spectroscopies are demonstrated to be powerful tools to unravel the electronic structure of solvated ions. In this work for the first time, we use a combination of these methods in the tender X-ray regime. This allowed us to address electronic transitions from deep core levels, to probe environmental effects, specifically in the bulk of the solution since the created energetic Auger electrons possess large mean free paths, and moreover, to obtain dynamical information about the ultrafast delocalization of the core-excited electron. In the considered exemplary aqueous KCl solution, the solvated isoelectronic K+ and Cl- ions exhibit notably different Auger electron spectra as a function of the photon energy. Differences appear due to dipole-forbidden transitions in aqueous K+ whose occurrence, according to the performed ab initio calculations, becomes possible only in the presence of solvent water molecules.
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| 5. |
- Ottosson, Niklas, et al.
(författare)
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Cations Strongly Reduce Electron Hopping-Times in Aqueous Solutions
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 133:34, s. 13489-13495
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Tidskriftsartikel (refereegranskat)abstract
- We study how the ultrafast electron transfer between H2O molecules in liquid water upon absorption of soft X-ray radiation depends on the local molecular binding environment. Our probe is the resonant Auger-decay of the water O1s core-hole (~3.6 fs), by which we show that efficiency for electron delocalization can be significantly reduced when a first-shell water molecule is replaced by an atomic ion. Decays resulting from excitations at the O1s post-edge feature (~540 eV) of 6m LiBr and 3m MgBr2 aqueous solutions reveal electron hopping-times of approximately 1.5 and 1.9 fs, respectively – the latter represents a four-fold increase compared to the corresponding value in neat water. The slower electron delocalization in electrolytes, which shows a strong dependence on the charge of the cations, can be explained by ion-induced reduction of water-water orbital mixing. Density functional theory (DFT) electronic structure calculations of solvation geometries obtained from molecular dynamics simulations reveal that this phenomenon largely arises from electrostatic perturbations of ions on the solvating water molecules. Our results demonstrate that it is possible to deliberately manipulate charge-transfer rates in aqueous media.
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| 6. |
- Ottosson, Niklas, et al.
(författare)
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Electronic rearrangement upon the hydrolyzation of aqueous formaldehyde studied by core-electron spectroscopies
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112:51, s. 16642-16646
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Tidskriftsartikel (refereegranskat)abstract
- We have combined near edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) to study the electronic rearrangement associated with the hydrolyzation of formaldehyde to methanediol in aqueous solution. The spectra are contrasted against those of aqueous formamide and urea, which are structurally similar but do not undergo hydrolysis in solution. We have recently demonstrated that the hydrolyzation of formaldehyde is manifested in the oxygen Is NEXAFS spectrum by the disappearance of the oxygen 1s -> pi* absorption line. This is a characteristic signature that the C=O double bond has been broken. In the present study we extend our investigation to include carbon Is NEXAFS and XPS spectra of the three solutions. The carbon NEXAFS spectra show the C 1s -> pi* absorption line for each solute except for formaldehyde. Moreover, the carbon Is photoelectron spectra exhibit a single peak for each solute. These observations point to a near complete hydrolyzation of formaldehyde, whereas formamide and urea remain intact in the solution. The analysis is further supported by density functional theory (DFT) calculations, showing a C Is chemical shift of approximately 1.0 eV between hydrolyzed and nonhydrolyzed forms, which would give distinguishable features in the photoemission spectrum, if coexisting forms were present in the solutions.
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| 7. |
- Ottosson, Niklas, et al.
(författare)
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Large variations in the propensity of aqueous oxychlorine anions for the solution/vapor interface
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:12, s. 124706-
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Tidskriftsartikel (refereegranskat)abstract
- Core-level photoelectron spectroscopy measurements have been performed of aqueous solutions of NaCl codissolved with NaClOn (n=1-4). Each species has a distinct Cl 2p electron binding energy, which can be exploited for depth-profiling experiments to study the competition between Cl-and ClOn- anions for residing in the outermost layers of the solution/vapor interface. Strongest propensity for the surface is observed for n=4 (perchlorate), followed by n=3 (chlorate), n=2 (chlorite), n=0 (chloride), and n=1 (hypochlorite). Molecular dynamics simulations rationalize the greatest surface propensity of the most oxidized anions in terms of their larger size and polarizability. The anomalous behavior of hypochlorite, being less surface-active than chloride, although it is both larger and more polarizable, is suggested to arise from the charge asymmetry over the anion, increasing its efficiency for bulk solvation. (C) 2009 American Institute of Physics. [doi:10.1063/1.3236805]
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| 8. |
- Ottosson, Niklas, et al.
(författare)
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On the Origins of Core-Electron Chemical Shifts of Small Biomolecules in Aqueous Solution : Insights from Photoemisson and ab Initio Calculations of Glycine(aq)
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 133:9, s. 3120-3130
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Tidskriftsartikel (refereegranskat)abstract
- The local electronic structure of glycine in neutral, basic, and acidic aqueous solution is studied experimentally by X-ray photoelectron spectroscopy and theoretically by molecular dynamics simulations accompanied by first-principle electronic structure and spectrum calculations. Measured and computed nitrogen and carbon is binding energies are assigned to different local atomic environments, which are shown to be sensitive to the protonation/deprotonation of the amino and carboxyl functional groups at different pH values. We report the first accurate computation of core-level chemical shifts of an aqueous solute in various protonation states and explicitly show how the distributions of photoelectron binding energies (core-level peak widths) are related to the details of the hydrogen bond configurations, i.e. the geometries of the water solvation shell and the associated electronic screening. The comparison between the experiments and calculations further enables the separation of protonation-induced (covalent) and solvent-induced (electrostatic) screening contributions to the chemical shifts in the aqueous phase. The present core-level line shape analysis facilitates an accurate interpretation of photoelectron spectra from larger biomolecular solutes than glycine.
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| 9. |
- Ottosson, Niklas, et al.
(författare)
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The influence of concentration on the molecular surface structure of simple and mixed aqueous electrolytes
- 2010
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 12:36, s. 10693-10700
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Tidskriftsartikel (refereegranskat)abstract
- We investigate various mechanisms contributing to the surface ion distributions in simple and mixed aqueous alkali-halide solutions depending on the total salt concentration, using a combination of photoelectron spectroscopy and molecular dynamics simulations. In simple solutions, the surface enhancement of large polarizable anions is reduced with increasing concentration. In the case of a NaBr/NaCl mixed aqueous solution, with bromide as the minority component, the situation is more complex. While the total anion/cation charge separation is similarly reduced with increasing salt content, this alone does not uniquely determine the ion distribution due to the co-existence of two different anions, Br- and Cl-. We show that bromide is selectively surface enhanced at higher concentrations, despite the fact that the total anion surface enhancement is reduced. This phenomenon, which can be viewed as "salting out'' of bromide by NaCl might have consequences for our understanding of the surface structure of mixed aqueous solutions subjected to concentration increase due to dehydration, such as seawater-born aerosols.
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| 10. |
- Ottosson, Niklas, et al.
(författare)
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The protonation state of small carboxylic acids at the water surface from photoelectron spectroscopy
- 2011
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 13:26, s. 12261-12267
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Tidskriftsartikel (refereegranskat)abstract
- We report highly surface sensitive core-level photoelectron spectra of small carboxylic acids (formic, acetic and butyric acid) and their respective carboxylate conjugate base forms (formate, acetate and butyrate) in aqueous solution. The relative surface propensity of the carboxylic acids and carboxylates is obtained by monitoring their respective C1s signal intensities from a solution in which their bulk concentrations are equal. All the acids are found to be enriched at the surface relative to the corresponding carboxylates. By monitoring the PE signals of acetic acid and acetate as a function of total concentration, we find that the protonation of acetic acid is nearly complete in the interface layer. This is in agreement with literature surface tension data, from which it is inferred that the acids are enriched at the surface while (sodium) formate and acetate, but not butyrate, are depleted. For butyric acid, we conclude that the carboxylate form co-exists with the acid in the interface layer. The free energy cost of replacing an adsorbed butyric acid molecule with a butyrate ion at 1.0 M concentration is estimated to be > 5 kJ mol(-1). By comparing concentration dependent surface excess data with the evolution of the corresponding photoemission signals it is furthermore possible to draw conclusions about how the distribution of molecules that contribute to the excess is altered with bulk concentration.
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