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| 2. |
- Ottosson, Niklas, et al.
(författare)
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An electronic signature of hydrolysation in the X-ray absorption spectrum of aqueous formaldehyde
- 2008
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 460:4-6, s. 540-542
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Tidskriftsartikel (refereegranskat)abstract
- Formaldehyde in aqueous solution is hydrolysed and forms methanediol. Using X-ray absorption spectroscopy we show that the hydrolysation product can be identified by a distinct electronic signature in the spectra. This is manifested by the disappearance of the oxygen 1s -> ; pi* absorption line. The X-ray absorption spectrum of aqueous formaldehyde is compared with those of the structurally similar formamide and urea, which are in contrast not hydrolysed in aqueous solution. We thereby demonstrate the exceptional sensitivity and simplicity of the technique to monitor this fundamental process in the aqueous phase.
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| 3. |
- Ottosson, Niklas, 1981-
(författare)
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Aqueous Solutions as seen through an Electron Spectrometer : Surface Structure, Hydration Motifs and Ultrafast Charge Delocalization Dynamics
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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 - PCCP. - 1463-9076 .- 1463-9084. ; 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 affinity 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-exist 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 >2.2 kBT. 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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| 9. |
- Pokapanich, Wandared, et al.
(författare)
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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
- 2012
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 116:1, s. 3-8
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Pokapanich, Wandared, et al.
(författare)
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Ionic charge dependence of ion-solvent ICD time-scale for aqueous ions probed by the core-hole clock
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Auger electron spectroscopy combined with theoretical calculations have been applied to investigate the decay of the Ca 2p core hole of aqueous Ca2+. Localized final states due to Auger-like and de-localized final states due to ICD-like decay processes are identified. By applying the core-hole clock spectroscopy method, the time constant of the ICD-like decay was determined to 24±6 fs for Ca2+. We have compared to ICD-like processes in other aqueous ions, K+, Na+, Mg2+ and Al3+, and observe a variation of the time constants of two orders of magnitude. This large variation is qualitatively explained by differences both internal and external to the ions; different internal decay mechanisms of the ions, as well as external differences in the ion-solute distances and interactions.
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