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  • 1.
    Björneholm, Olle
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Werner, Josephina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ottosson, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Öhrwall, Gunnar
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Winter, Bernd
    Unger, Isaak
    Söderström, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Deeper Insight into Depth-Profiling of Aqueous Solutions Using Photoelectron Spectroscopy2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 50, p. 29333-29339Article in journal (Refereed)
    Abstract [en]

    X-ray photoelectron spectroscopy (XPS) is widely used to probe properties such as molecular stoichiometry, microscopic distributions relative to the surface by so-called "depth-profiling", and molecular orientation. Such studies usually rely on the core-level photoionization cross sections being independent of molecular composition. The validity of this assumption has recently been questioned, as a number of gas-phase molecules have been shown to exhibit photon-energy-dependent nonstochiometric intensity oscillations arising from EXAFS-like modulations of the photoionization cross section. We have studied this phenomenon in trichloroethanol in both gas phase and dissolved in water. The gas-phase species exhibits pronounced intensity oscillations, similar to the ones observed for other gas-phase molecules. These oscillations are also observed for the dissolved species, implying that the effect has to be taken into account when performing depth-profiling experiments of solutions and other condensed matter systems. The similarity between the intensity oscillations for gas phase and dissolved species allows us to determine the photoelectron kinetic energy of maximum surface sensitivity, ~100 eV, which lies in the range of pronounced intensity oscillations.

  • 2.
    Couto, Rafael C.
    et al.
    Royal Inst Technol, Sch Biotechnol, Theoret Chem & Biol, SE-10691 Stockholm, Sweden.;Univ Fed Goias, Inst Quim, Campus Samambaia,CP 131, BR-74001970 Goiania, Go, Brazil..
    Guarise, Marco
    Lab Nacl Luz Sincrotron, BR-10000 Campinas, SP, Brazil.;Univ Paris 06, Univ Paris 04, UMR7614, Lab Chim Phys Mat & Rayonnement, F-75005 Paris, France..
    Nicolaou, Alessandro
    Synchrotron SOLEIL, Boite Postale 48, F-91192 Gif Sur Yvette, France..
    Jaouen, Nicolas
    Synchrotron SOLEIL, Boite Postale 48, F-91192 Gif Sur Yvette, France..
    Chiuzbaian, Gheorghe S.
    Univ Paris 06, Univ Paris 04, UMR7614, Lab Chim Phys Mat & Rayonnement, F-75005 Paris, France..
    Luening, Jan
    Univ Paris 06, Univ Paris 04, UMR7614, Lab Chim Phys Mat & Rayonnement, F-75005 Paris, France..
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sathe, Conny
    Lund Univ, MAX Lab 4, Box 118, SE-22100 Lund, Sweden..
    Hennies, Franz
    Lund Univ, MAX Lab 4, Box 118, SE-22100 Lund, Sweden..
    Guimaraes, Freddy F.
    Univ Fed Goias, Inst Quim, Campus Samambaia,CP 131, BR-74001970 Goiania, Go, Brazil..
    Agren, Hans
    Royal Inst Technol, Sch Biotechnol, Theoret Chem & Biol, SE-10691 Stockholm, Sweden..
    Gel'mukhanov, Faris
    Royal Inst Technol, Sch Biotechnol, Theoret Chem & Biol, SE-10691 Stockholm, Sweden..
    Journel, Loic
    Univ Paris 06, Univ Paris 04, UMR7614, Lab Chim Phys Mat & Rayonnement, F-75005 Paris, France..
    Simon, Marc
    Univ Paris 06, Univ Paris 04, UMR7614, Lab Chim Phys Mat & Rayonnement, F-75005 Paris, France..
    Kimberg, Victor
    Royal Inst Technol, Sch Biotechnol, Theoret Chem & Biol, SE-10691 Stockholm, Sweden..
    Coupled electron-nuclear dynamics in resonant 1 sigma -> 2 pi x-ray Raman scattering of CO molecules2016In: PHYSICAL REVIEW A, ISSN 2469-9926, Vol. 93, no 3, article id 032510Article in journal (Refereed)
    Abstract [en]

    We present a detailed experimental-theoretical analysis of O K-edge resonant 1 sigma-2 pi inelastic x-ray scattering (RIXS) from carbon monoxide with unprecedented energy resolution. We employ high-level ab initio calculations to compute the potential energy curves of the states involved in the RIXS process and simulate the measured RIXS spectra using the wave-packet-propagation formalism, including Coulomb coupling in the final-state manifold. The theoretical analysis allows us to explain all the key features of the experimental spectra, including some that were not seen before. First, we clearly show the interference effect between different RIXS channels corresponding to the transition via orthogonal (1)Pi(x) and (1)Pi(y) core-excited states of CO. Second, the RIXS region of 13 eV energy loss presents a triple structure, revealed only by the high-resolution measurement. In previous studies, this region was attributed solely to a valence state. Here we show a strong Coulomb mixing of the Rydberg and valence final states, which opens the forbidden RIXS channels to the "dark" final Rydberg states and drastically changes the RIXS profile. Third, using a combination of high-resolution experiment and high-level theory, we improve the vertical bar 4 sigma(-1)2 pi(1)> final-state potential-energy curve by fitting its bottom part with the experiment. Also, the coupling constants between Rydberg and valence states were refined via comparison with the experiment. Our results illustrate the large potential of the RIXS technique for advanced studies of highly excited states of neutral molecules.

  • 3.
    Couto, Rafael C.
    et al.
    Royal Inst Technol, Sch Biotechnol, Theoret Chem & Biol, S-10691 Stockholm, Sweden.;Univ Fed Goias, Inst Quim, Campus Samambaia,CP 131, BR-74001970 Goiania, Go, Brazil..
    Guarise, Marco
    Lab Nacl Luz Sincrotron, BR-10000 Campinas, Brazil.;Univ Paris 06, Univ Paris 04, Lab Chim Phys Matiere & Rayonnement, UMR7614, F-75005 Paris, France..
    Nicolaou, Alessandro
    Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Jaouen, Nicolas
    Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Chiuzbaian, Gheorghe S.
    Univ Paris 06, Univ Paris 04, Lab Chim Phys Matiere & Rayonnement, UMR7614, F-75005 Paris, France..
    Luening, Jan
    Univ Paris 06, Univ Paris 04, Lab Chim Phys Matiere & Rayonnement, UMR7614, F-75005 Paris, France..
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Sathe, Conny
    Lund Univ, MAX Lab 4, Box 118, S-22100 Lund, Sweden..
    Hennies, Franz
    Lund Univ, MAX Lab 4, Box 118, S-22100 Lund, Sweden..
    Kimberg, Victor
    Royal Inst Technol, Sch Biotechnol, Theoret Chem & Biol, S-10691 Stockholm, Sweden..
    Guimaraes, Freddy F.
    Univ Fed Goias, Inst Quim, Campus Samambaia,CP 131, BR-74001970 Goiania, Go, Brazil..
    Agren, Hans
    Royal Inst Technol, Sch Biotechnol, Theoret Chem & Biol, S-10691 Stockholm, Sweden..
    Gel'mukhanov, Faris
    Royal Inst Technol, Sch Biotechnol, Theoret Chem & Biol, S-10691 Stockholm, Sweden..
    Journel, Loic
    Univ Paris 06, Univ Paris 04, Lab Chim Phys Matiere & Rayonnement, UMR7614, F-75005 Paris, France..
    Simon, Marc
    Univ Paris 06, Univ Paris 04, Lab Chim Phys Matiere & Rayonnement, UMR7614, F-75005 Paris, France..
    Anomalously strong two-electron one-photon X-ray decay transitions in CO caused by avoided crossing2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 20947Article in journal (Refereed)
    Abstract [en]

    The unique opportunity to study and control electron-nuclear quantum dynamics in coupled potentials offered by the resonant inelastic X-ray scattering (RIXS) technique is utilized to unravel an anomalously strong two-electron one-photon transition from core-excited to Rydberg final states in the CO molecule. High-resolution RIXS measurements of CO in the energy region of 12-14 eV are presented and analyzed by means of quantum simulations using the wave packet propagation formalism and ab initio calculations of potential energy curves and transition dipole moments. The very good overall agreement between the experimental results and the theoretical predictions allows an in-depth interpretation of the salient spectral features in terms of Coulomb mixing of "dark" with "bright" final states leading to an effective two-electron one-photon transition. The present work illustrates that the improved spectral resolution of RIXS spectra achievable today may call for more advanced theories than what has been used in the past.

  • 4.
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ion pairing and Langmuir-like adsorption at aqueous surfaces studied by core-level spectroscopy2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Surface-bulk equilibria for solutes in aqueous solutions are studied using X-ray Photoelectron Spectroscopy (XPS) with high surface and chemical sensitivity. In the first part, the results show a reduction of the biochemically relevant guanidinium ions’ surface propensity with the addition of disodium sulphate due to ion pairing with the strongly hydrated sulphate ion, which could have implications for protein folding. Thereafter, the work considers amphiphilic organic compounds related to atmospheric science where the surface propensities, orientations at the surface and solute-solute and solute-solvent interactions are investigated. In the second part, two linear organic ions are investigated both as single solutes and in mixture. Both organic ions are surface enriched on their own and even more in the mixed solute solution. Due to hydrophobic expulsion of the alkyl chains, ion pairing between the organic ions and van der Waals interaction, the organic ions seem to assemble in clusters with their alkyl chains pointing out of the surface. The third part also covers linear organic compounds but one at a time probing the surface concentration as a function of bulk concentration. A Langmuir-like adsorption behavior was observed and Gibb’s free energy of surface adsorption (ΔGAds) values were extracted. An empiric model for deriving values for ΔGAds is proposed based upon the seemingly linear change in ΔGAds per carbon when comparing alcohols of different chain lengths. The fourth part investigates the acid/base fraction at the surface as function of bulk pH. The most important factor for this fraction seems to be how the surface propensity varies with the charge state of the acid or base instead of a possible difference in pH or pKa value at the surface. In the fifth part the oxygen K-edge of aqueous carbonate and bicarbonate is probed with the bulk-sensitive Resonant Inelastic X-ray Scattering (RIXS) technique.

    List of papers
    1. Anomalous surface behavior of hydrated guanidinium ions due to ion pairing
    Open this publication in new window or tab >>Anomalous surface behavior of hydrated guanidinium ions due to ion pairing
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    2018 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 14, article id 144508Article in journal (Refereed) Published
    Abstract [en]

    Surface affinity of aqueous guanidinium chloride (GdmCl) is compared to that of aqueous tetrapropylammonium chloride (TPACl) upon addition of sodium chloride (NaCl) or disodium sulfate (Na2SO4). The experimental results have been acquired using the surface sensitive technique X-ray photoelectron spectroscopy on a liquid jet. Molecular dynamics simulations have been used to produce radial distribution functions and surface density plots. The surface affinities of both TPA(+) and Gdm(+) increase upon adding NaCl to the solution. With the addition of Na2SO4, the surface affinity of TPA(+) increases, while that of Gdm(+) decreases. From the results of MD simulations it is seen that Gdm(+) and SO42- ions form pairs. This finding can be used to explain the decreased surface affinity of Gdm(+) when co-dissolved with SO42- ions. Since SO42- ions avoid the surface due to the double charge and strong water interaction, the Gdm(+)-SO42- ion pair resides deeper in the solutions' bulk than the Gdm(+) ions. Since TPA(+) does not form ion pairs with SO42-, the TPA(+) ions are instead enriched at the surface.

    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-353201 (URN)10.1063/1.5024348 (DOI)000430128600034 ()29655316 (PubMedID)
    Funder
    Swedish Research Council
    Available from: 2018-06-13 Created: 2018-06-13 Last updated: 2018-09-02Bibliographically approved
    2. Strong Enrichment of Atmospherically Relevant Organic Ions at the Aqueous Interface: The Role of Ion Pairing and Cooperative Effects
    Open this publication in new window or tab >>Strong Enrichment of Atmospherically Relevant Organic Ions at the Aqueous Interface: The Role of Ion Pairing and Cooperative Effects
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    2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 42, p. 27185-27191Article in journal (Refereed) Published
    Abstract [en]

    Surface affinity, orientation and ion pairing are investigated in mixed and single solute systems of aqueous sodium hexanoate and hexylammonium chloride. The surface sensitive X-ray photoelectron spectroscopy technique has been used to acquire the experimental results, while the computational data have been calculated using molecular dynamics simulations. By comparing the single solute solutions with the mixed one, we observe a non-linear surface enrichment and reorientation of the organic ions with their alkyl chains pointing out of the aqueous surface. We ascribe this effect to ion paring between the charged functional groups on the respective organic ion and hydrophobic expulsion of the alkyl chains from the surface in combination with van der Waals interactions between the alkyl chains. These cooperative effects lead to a substantial surface enrichment of organic ions, with consequences for aerosol surface properties.

    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:uu:diva-357368 (URN)10.1039/c8cp04525a (DOI)000451351500042 ()30339167 (PubMedID)
    Funder
    Swedish Research Council, 2013-3940Swedish Research Council, 2014-04518Carl Tryggers foundation
    Available from: 2018-08-15 Created: 2018-08-15 Last updated: 2019-01-07Bibliographically approved
    3. Surface propensity of atmospherically relevant carboxylates and alkyl ammonium ions studied by XPS: towards a building-block model of surface propensity based on Langmuir adsorption
    Open this publication in new window or tab >>Surface propensity of atmospherically relevant carboxylates and alkyl ammonium ions studied by XPS: towards a building-block model of surface propensity based on Langmuir adsorption
    Show others...
    (English)Manuscript (preprint) (Other academic)
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:uu:diva-358541 (URN)
    Available from: 2018-08-30 Created: 2018-08-30 Last updated: 2018-09-02
    4. Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers
    Open this publication in new window or tab >>Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers
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    2015 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 21, p. 14036-14044Article in journal (Refereed) Published
    Abstract [en]

    Position isomerism is ubiquitous in atmospheric oxidation reactions. Therefore, we have compared surface-active oxygenated amphiphilic isomers (1- and 3-pentanol) at the aqueous surface with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. The experimental data are complemented with molecular dynamics (MD) simulations. A concentration-dependent orientation and solvation of the amphiphiles at the aqueous surface is observed. At bulk concentrations as low as around 100 mM, a monolayer starts to form for both isomers, with the hydroxyl groups pointing towards the bulk water and the alkyl chains pointing towards the vacuum. The monolayer (ML) packing density of 3-pentanol is approx. 70% of the one observed for 1-pentanol, with a molar surface concentration that is approx. 90 times higher than the bulk concentration for both molecules. The molecular area at ML coverage (approximate to 100 mM) was calculated to be around 32 +/- 2 angstrom(2) per molecule for 1-pentanol and around 46 +/- 2 angstrom(2) per molecule for 3-pentanol, which results in a higher surface concentration (molecules per cm(2)) for the linear isomer. In general we conclude therefore that isomers - with comparable surface activities - that have smaller molecular areas will be more abundant at the interface in comparison to isomers with larger molecular areas, which might be of crucial importance for the understanding of key properties of aerosols, such as evaporation and uptake capabilities as well as their reactivity.

    National Category
    Physical Chemistry Physical Sciences
    Identifiers
    urn:nbn:se:uu:diva-256562 (URN)10.1039/c5cp01870f (DOI)000354946200029 ()25953683 (PubMedID)
    Available from: 2015-06-24 Created: 2015-06-24 Last updated: 2018-09-02Bibliographically approved
    5. Alcohols at the Aqueous Surface: Chain Length and Isomer Effects
    Open this publication in new window or tab >>Alcohols at the Aqueous Surface: Chain Length and Isomer Effects
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    2016 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 9, p. 6648-6656Article in journal (Refereed) Published
    Abstract [en]

    Surface-active organic molecules at the liquid-vapor interface are of great importance in atmospheric science. Therefore, we studied the surface behavior of alcohol isomers with different chain lengths (C4-C6) in aqueous solution with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. Gibbs free energies of adsorption and surface concentrations are determined from the XPS results using a standard Langmuir adsorption isotherm model. The free energies of adsorption, ranging from around -15 to -19 kJ/mol (C4-C6), scale linearly with the number of carbon atoms within the alcohols with ΔGAds/CH2 ≈ -2 kJ/mol. While for the linear alcohols, surface concentrations lie around 2.4 x 1014 molecules/cm2 at the bulk concentrations where monolayers are formed, the studied branched alcohols show lower surface concentrations of around 1.6 x 1014 molecules/cm2, both of which are in line with the molecular structure and their orientation at the interface. Interestingly, we find that there is a maximum in the surface enrichment factor for linear alcohols at low concentrations, which is not observed for the shorter branched alcohols. This is interpreted in terms of a cooperative effect, which we suggest to be the result of more effective van der Waals interactions between the linear alcohol alkyl chains at the aqueous surface, making it energetically even more favorable to reside at the liquid-vapor interface. 

    National Category
    Physical Chemistry Condensed Matter Physics
    Identifiers
    urn:nbn:se:uu:diva-265221 (URN)10.1039/c5cp06463e (DOI)000371139400030 ()26868637 (PubMedID)
    Funder
    Swedish Research CouncilSwedish Foundation for Strategic Research Carl Tryggers foundation
    Available from: 2015-10-26 Created: 2015-10-26 Last updated: 2018-09-02Bibliographically approved
    6. Shifted Equilibria of Organic Acids and Bases in the Aqueous Surface Region
    Open this publication in new window or tab >>Shifted Equilibria of Organic Acids and Bases in the Aqueous Surface Region
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    2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 36, p. 23281-23293Article in journal (Refereed) Published
    Abstract [en]

    Acid-base equilibria of carboxylic acids and alkyl amines in the aqueous surface region were studied using surface-sensitive X-ray photoelectron spectroscopy and molecular dynamics simulations. Solutions of these organic compounds were examined as a function of pH, concentration and chain length to investigate the distribution of acid and base form in the surface region as compared to the aqueous bulk. Results from these experiments show that the neutral forms of the studied acid-base pairs are strongly enriched in the aqueous surface region. Moreover, we show that for species with at least four carbon atoms in their alkyl-chain, their charged forms are also found to be abundant in the surface region. Using a combination of XPS and MD results, a model is proposed that effectively describes the surface composition. Resulting absolute surface concentration estimations show clearly that the total organic mole fractions in the surface region change drastically as a function of solution pH. The origin of the observed surface phenomena, hydronium/hydroxide concentrations in the aqueous surface region and why standard chemical equations, used to describe equilibria in dilute bulk solution are not valid in the aqueous surface region, are discussed in detail. The reported results are of considerable importance especially for the detailed understanding of properties of small aqueous droplets that can be found in the atmosphere.

    National Category
    Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-341965 (URN)10.1039/c8cp01898g (DOI)000447370600011 ()30191936 (PubMedID)
    Funder
    Swedish Research Council, 2013-3940EU, Horizon 2020, 717022
    Available from: 2018-02-16 Created: 2018-02-16 Last updated: 2019-01-22Bibliographically approved
    7. Aqueous carbonate and bicarbonate ions studied by RIXS at the O K-edge
    Open this publication in new window or tab >>Aqueous carbonate and bicarbonate ions studied by RIXS at the O K-edge
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    (English)Manuscript (preprint) (Other academic)
    National Category
    Atom and Molecular Physics and Optics
    Identifiers
    urn:nbn:se:uu:diva-359428 (URN)
    Available from: 2018-09-02 Created: 2018-09-02 Last updated: 2018-09-02
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  • 5.
    Ekholm, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Caleman, C
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Molecular biophysics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Walz, Marie-Madeleine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational Biology and Bioinformatics.
    Werner, Josephina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Öhrwall, Gunnar
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Surface propensity of atmospherically relevant carboxylates and alkyl ammonium ions studied by XPS: towards a building-block model of surface propensity based on Langmuir adsorptionManuscript (preprint) (Other academic)
  • 6.
    Ekholm, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. DESY, Ctr Free Elec Laser Sci, Notkestr 85, DE-22607 Hamburg, Germany.
    Bjärnhall Prytz, Nicklas
    Royal Inst Tech, Dept App Phys, Roslagstullsbacken 21, SE-11421 Stockholm, Sweden.
    Walz, Marie-Madeleine
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational Biology and Bioinformatics.
    Werner, Josephina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Öhrwall, Gunnar
    Lund Univ, MAX Lab 4, Box 118, SE-22100 Lund, Sweden.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Strong Enrichment of Atmospherically Relevant Organic Ions at the Aqueous Interface: The Role of Ion Pairing and Cooperative Effects2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 42, p. 27185-27191Article in journal (Refereed)
    Abstract [en]

    Surface affinity, orientation and ion pairing are investigated in mixed and single solute systems of aqueous sodium hexanoate and hexylammonium chloride. The surface sensitive X-ray photoelectron spectroscopy technique has been used to acquire the experimental results, while the computational data have been calculated using molecular dynamics simulations. By comparing the single solute solutions with the mixed one, we observe a non-linear surface enrichment and reorientation of the organic ions with their alkyl chains pointing out of the aqueous surface. We ascribe this effect to ion paring between the charged functional groups on the respective organic ion and hydrophobic expulsion of the alkyl chains from the surface in combination with van der Waals interactions between the alkyl chains. These cooperative effects lead to a substantial surface enrichment of organic ions, with consequences for aerosol surface properties.

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    fulltext
  • 7.
    Ekholm, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Dong, Minjie
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Såthe, Conny
    Uppsala University.
    Chatzigeorgiou, Evanthia
    Agåker, Marcus
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Harada, Yoshihisa
    Miyawaki, Jun
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Aqueous carbonate and bicarbonate ions studied by RIXS at the O K-edgeManuscript (preprint) (Other academic)
  • 8.
    Ekholm, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala Univ, Dept Phys & Astron, POB 516, SE-75120 Uppsala, Sweden.
    Vazdar, Mario
    Rudjer Boskovic Inst, Bijenicka Cesta 54, Zagreb 10000, Croatia.
    Mason, Philip E.
    Acad Sci Czech Republ, Inst Organ Chem & Biochem, Flemingovo Nam 2, CR-16610 Prague 6, Czech Republic.
    Bialik, Erik
    Lund Univ, Dept Chem, Phys Chem, POB 124, SE-22100 Lund, Sweden.
    Walz, Marie-Madeleine
    Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational Biology and Bioinformatics. Uppsala Univ, Dept Cell & Mol Biol Computat Biol & Bioinformat, POB 596, SE-75124 Uppsala, Sweden.
    Ohrwall, Gunnar
    Lund Univ, MAX Lab 4, POB 118, SE-22100 Lund, Sweden.
    Werner, Josephina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Jungwirth, Pavel
    Acad Sci Czech Republ, Inst Organ Chem & Biochem, Flemingovo Nam 2, CR-16610 Prague 6, Czech Republic.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Anomalous surface behavior of hydrated guanidinium ions due to ion pairing2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 14, article id 144508Article in journal (Refereed)
    Abstract [en]

    Surface affinity of aqueous guanidinium chloride (GdmCl) is compared to that of aqueous tetrapropylammonium chloride (TPACl) upon addition of sodium chloride (NaCl) or disodium sulfate (Na2SO4). The experimental results have been acquired using the surface sensitive technique X-ray photoelectron spectroscopy on a liquid jet. Molecular dynamics simulations have been used to produce radial distribution functions and surface density plots. The surface affinities of both TPA(+) and Gdm(+) increase upon adding NaCl to the solution. With the addition of Na2SO4, the surface affinity of TPA(+) increases, while that of Gdm(+) decreases. From the results of MD simulations it is seen that Gdm(+) and SO42- ions form pairs. This finding can be used to explain the decreased surface affinity of Gdm(+) when co-dissolved with SO42- ions. Since SO42- ions avoid the surface due to the double charge and strong water interaction, the Gdm(+)-SO42- ion pair resides deeper in the solutions' bulk than the Gdm(+) ions. Since TPA(+) does not form ion pairs with SO42-, the TPA(+) ions are instead enriched at the surface.

  • 9.
    Marinho, Ricardo R. T.
    et al.
    Univ Fed Bahia, Inst Phys, BR-40170115 Salvador, BA, Brazil..
    Walz, Marie-Madeleine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational Biology and Bioinformatics.
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ohrwall, Gunnar
    Lund Univ, MAX Lab 4, POB 118, SE-22100 Lund, Sweden..
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    de Brito, Arnaldo Naves
    Univ Estadual Campinas, Inst Phys Gleb Wataghin, BR-13083859 Campinas, SP, Brazil..
    Ethanol Solvation in Water Studied on a Molecular Scale by Photoelectron Spectroscopy2017In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 121, no 33, p. 7916-7923Article in journal (Refereed)
    Abstract [en]

    Because of the amphiphilic properties of alcohols, hydrophobic hydration is important in the alcohol water system. In the present paper we employ X-ray photoelectron spectroscopy (XPS) to investigate the bulk and surface molecular structure of ethanol water mixtures from 0.2 to 95 mol %. The observed XPS binding energy splitting between the methyl C is and hydroxymethyl C is groups (BES_[CH3-CH2OH]) as a function of the ethanol molar percentage can be divided into different regions: one below 35 mol % with higher values (about 1.53 eV) and one starting at 60 mol % up to 95 mol % with 1.49 eV as an average value. The chemical shifts agree with previous quantum mechanics/molecular mechanics (QM/MM) calculations [Loytynoja, T.; et al. J. Phys. Chem. B 2014, 118, 13217]. According to these calculations, the BES_[CH3-CH2OH] is related to the number of hydrogen bonds between the ethanol and the surrounding molecules. As the ethanol concentration increases, the average number of hydrogen bonds decreases from 2.5 for water-rich mixtures to 2 for pure ethanol. We give an interpretation for this behavior based on how the hydrogen bonds are distributed according to the mixing ratio. Since our experimental data are surface sensitive, we propose that this effect may also be manifested at the interface. From the ratio between the XPS C is core lines intensities we infer that below 20 mol % the ethanol molecules have their hydroxyl groups more hydrated and possibly facing the solution's bulk. Between 0.1 and 14 mol %, we show the formation of an ethanol monolayer at approximately 2 mol %. Several parameters are derived for the surface region at monolayer coverage.

  • 10. Ohrwall, Gunnar
    et al.
    Prisle, Nonne L.
    Ottosson, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Werner, Josephina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Walz, Marie-Madeleine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Acid-Base Speciation of Carboxylate Ions in the Surface Region of Aqueous Solutions in the Presence of Ammonium and Aminium Ions2015In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 119, no 10, p. 4033-4040Article in journal (Refereed)
    Abstract [en]

    The acid base speciation of surface-active carboxylate ions in the surface region of aqueous solutions was studied with synchrotron-radiation-based photoelectron spectroscopy. The protonated form was found at an extraordinarily large fraction compared to that expected from the bulk pH. When adding salts containing the weak acid NH4+ to the solution, the fraction of the acidic form at the surface increases, and to a Much greatet extent than expected from the bulk pH of the solution. We show that ammonium ions also are overrepresented in the surface region, and propose that the interaction between the surface-active anionic carboxylates and cationic ammonium ions creates a carboxylateammonium bilayer close to the surface, which increases the probability of the protonation of the carboxylae ions. By comparing the situation when a salt of the less volatile amine diethanolatnine is used, We also show that the observed evaporation of ammonia that occurs after such an event only affects the equilibrium marginally.

  • 11.
    Walz, Marie-Madeleine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Werner, Josephina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Lundberg, D.
    Prisle, N. L.
    Ohrwall, G.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Surface behavior of amphiphiles in aqueous solution: a comparison between different pentanol isomers2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 21, p. 14036-14044Article in journal (Refereed)
    Abstract [en]

    Position isomerism is ubiquitous in atmospheric oxidation reactions. Therefore, we have compared surface-active oxygenated amphiphilic isomers (1- and 3-pentanol) at the aqueous surface with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. The experimental data are complemented with molecular dynamics (MD) simulations. A concentration-dependent orientation and solvation of the amphiphiles at the aqueous surface is observed. At bulk concentrations as low as around 100 mM, a monolayer starts to form for both isomers, with the hydroxyl groups pointing towards the bulk water and the alkyl chains pointing towards the vacuum. The monolayer (ML) packing density of 3-pentanol is approx. 70% of the one observed for 1-pentanol, with a molar surface concentration that is approx. 90 times higher than the bulk concentration for both molecules. The molecular area at ML coverage (approximate to 100 mM) was calculated to be around 32 +/- 2 angstrom(2) per molecule for 1-pentanol and around 46 +/- 2 angstrom(2) per molecule for 3-pentanol, which results in a higher surface concentration (molecules per cm(2)) for the linear isomer. In general we conclude therefore that isomers - with comparable surface activities - that have smaller molecular areas will be more abundant at the interface in comparison to isomers with larger molecular areas, which might be of crucial importance for the understanding of key properties of aerosols, such as evaporation and uptake capabilities as well as their reactivity.

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  • 12.
    Walz, Marie-Madeleine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Werner, Josephina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics. Swedish University for Agricultural Sciences, Department of Chemistry and Biotechnology.
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Prisle, N. L.
    Helsinki University, Department of Physics.
    Öhrwall, Gunnar
    Lund University, MAX IV Laboratory.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Alcohols at the Aqueous Surface: Chain Length and Isomer Effects2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 9, p. 6648-6656Article in journal (Refereed)
    Abstract [en]

    Surface-active organic molecules at the liquid-vapor interface are of great importance in atmospheric science. Therefore, we studied the surface behavior of alcohol isomers with different chain lengths (C4-C6) in aqueous solution with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. Gibbs free energies of adsorption and surface concentrations are determined from the XPS results using a standard Langmuir adsorption isotherm model. The free energies of adsorption, ranging from around -15 to -19 kJ/mol (C4-C6), scale linearly with the number of carbon atoms within the alcohols with ΔGAds/CH2 ≈ -2 kJ/mol. While for the linear alcohols, surface concentrations lie around 2.4 x 1014 molecules/cm2 at the bulk concentrations where monolayers are formed, the studied branched alcohols show lower surface concentrations of around 1.6 x 1014 molecules/cm2, both of which are in line with the molecular structure and their orientation at the interface. Interestingly, we find that there is a maximum in the surface enrichment factor for linear alcohols at low concentrations, which is not observed for the shorter branched alcohols. This is interpreted in terms of a cooperative effect, which we suggest to be the result of more effective van der Waals interactions between the linear alcohol alkyl chains at the aqueous surface, making it energetically even more favorable to reside at the liquid-vapor interface. 

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  • 13.
    Werner, Josephina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Department of Molecular Sciences, Swedish University of Agricultural Sciences, Box 7015, SE-750 07 Uppsala, Sweden.
    Persson, Ingmar
    Department of Molecular Sciences, Swedish University of Agricultural Sciences, Box 7015, SE-750 07 Uppsala, Sweden.
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Kawecki, Delphine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Saak, Clara-Magdalena
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Walz, Marie-Madeleine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Unger, Isaak
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Valtl, Corina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Caleman, Carl
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Center for Free-Electron Laser Science, Deutsches Elektronen-Synchrotron, Notkestraße 85, DE-22607 Hamburg, Germany.
    Öhrwall, Gunnar
    MAX IV Laboratory, Lund University, Box 118, SE-22100 Lund, Sweden.
    Prisle, Nonne L.
    Univ Oulu, Nano & Mol Syst Res Unit, Fac Sci, Box 3000, FI-90014 Oulu, Finland;Univ Helsinki, Div Atmospher Sci, Dept Phys, Box 64, FI-00014 Helsinki, Finland.
    Shifted Equilibria of Organic Acids and Bases in the Aqueous Surface Region2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 36, p. 23281-23293Article in journal (Refereed)
    Abstract [en]

    Acid-base equilibria of carboxylic acids and alkyl amines in the aqueous surface region were studied using surface-sensitive X-ray photoelectron spectroscopy and molecular dynamics simulations. Solutions of these organic compounds were examined as a function of pH, concentration and chain length to investigate the distribution of acid and base form in the surface region as compared to the aqueous bulk. Results from these experiments show that the neutral forms of the studied acid-base pairs are strongly enriched in the aqueous surface region. Moreover, we show that for species with at least four carbon atoms in their alkyl-chain, their charged forms are also found to be abundant in the surface region. Using a combination of XPS and MD results, a model is proposed that effectively describes the surface composition. Resulting absolute surface concentration estimations show clearly that the total organic mole fractions in the surface region change drastically as a function of solution pH. The origin of the observed surface phenomena, hydronium/hydroxide concentrations in the aqueous surface region and why standard chemical equations, used to describe equilibria in dilute bulk solution are not valid in the aqueous surface region, are discussed in detail. The reported results are of considerable importance especially for the detailed understanding of properties of small aqueous droplets that can be found in the atmosphere.

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  • 14.
    Werner, Josephina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Wernersson, Erik
    Ekholm, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ottosson, Niklas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Ohrwall, Gunnar
    Heyda, Jan
    Persson, Ingmar
    Söderström, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Jungwirth, Pavel
    Björneholm, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Surface Behavior of Hydrated Guanidinium and Ammonium Ions: A Comparative Study by Photoelectron Spectroscopy and Molecular Dynamics2014In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 118, no 25, p. 7119-7127Article in journal (Refereed)
    Abstract [en]

    Through the combination of surface sensitive photoelectron spectroscopy and molecular dynamics simulation, the relative surface propensities of guanidinium and ammonium ions in aqueous solution are characterized. The fact that the N Is binding energies differ between these two species was exploited to monitor their relative surface concentration through their respective photoemission intensities. Aqueous solutions of ammonium and guanidinium chloride, and mixtures of these salts, have been studied in a wide concentration range, and it is found that the guanidinium ion has a greater propensity to reside at the aqueous surface than the ammonium ion. A large portion of the relative excess of guanidinium ions in the surface region of the mixed solutions can be explained by replacement of ammonium ions by guanidinium ions in the surface region in combination with a strong salting-out effect of guanidinium by ammonium ions at increased concentrations. This interpretation is supported by molecular dynamics simulations, which reproduce the experimental trends very well. The simulations suggest that the relatively higher surface propensity of guanidinium compared with ammonium ions is due to the ease of dehydration of the faces of the almost planar guanidinium ion, which allows it to approach the water-vapor interface oriented parallel to it.

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