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  • 1. Achari, Muthuraaman Bhagavathi
    et al.
    Elumalai, Viswanathan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vlachopoulos, Nick
    Safdari, Majid
    Gao, Jiajia
    Gardner, James M.
    Kloo, Lars
    A quasi-liquid polymer-based cobalt redox mediator electrolyte for dye-sensitized solar cells2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 40, p. 17419-17425Article in journal (Refereed)
    Abstract [en]

    Recently, cobalt redox electrolyte mediators have emerged as a promising alternative to the commonly used iodide/triiodide redox shuttle in dye-sensitized solar cells (DSCs). Here, we report the successful use of a new quasi-liquid, polymer-based electrolyte containing the Co3+/Co2+ redox mediator in 3-methoxy propionitrile solvent in order to overcome the limitations of high cell resistance, low diffusion coefficient and rapid recombination losses. The performance of the solar cells containing the polymer based electrolytes increased by a factor of 1.2 with respect to an analogous electrolyte without the polymer. The performances of the fabricated DSCs have been investigated in detail by photovoltaic, transient electron measurements, EIS, Raman and UV-vis spectroscopy. This approach offers an effective way to make high-performance and long-lasting DSCs.

  • 2. Aidas, Kestutis
    et al.
    Agren, Hans
    Kongsted, Jacob
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Mocci, Francesca
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    A quantum mechanics/molecular dynamics study of electric field gradient fluctuations in the liquid phase. the case of na+ in aqueous solution2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 5, p. 1621-1631Article in journal (Refereed)
    Abstract [en]

    The Na-23 quadrupolar coupling constant of the Na+ ion in aqueous solution has been predicted using molecular dynamics simulations and hybrid quantum mechanics/molecular mechanics methods for the calculation of electric field gradients. The developed computational approach is generally expected to provide reliable estimates of the quadrupolar coupling constants of monoatomic species in condensed phases, and we show here that intermolecular polarization and non-electrostatic interactions are of crucial importance as they result in a 100% increased quadrupolar coupling constant of the ion as compared to a simpler pure electrostatic picture. These findings question the reliability of the commonly applied classical Sternheimer approximation for the calculations of the electric field gradient. As it can be expected from symmetry considerations, the quadrupolar coupling constants of the 5- and 6-coordinated Na+ ions in solution are found to differ significantly.

  • 3. Anniyev, Toyli
    et al.
    Ogasawara, Hirohito
    Ljungberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Wikfeldt, Kjartan T.
    Stockholm University, Faculty of Science, Department of Physics.
    MacNaughton, Janay B.
    Näslund, Lars-Åke
    Bergmann, Uwe
    Koh, Shirlaine
    Strasser, Peter
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Complementarity between high-energy photoelectron and L-edge spectroscopy for probing the electronic structure of 5d transition metal catalysts2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 21, p. 5694-5700Article in journal (Refereed)
    Abstract [en]

    We demonstrate the successful use of hard X-ray photoelectron spectroscopy (HAXPES) for selectively probing the platinum partial d-density of states (DOS) in a Pt-Cu nanoparticle catalyst which shows activity superior to pure Pt towards the oxygen-reduction reaction (ORR). The information about occupied Pt d-band states was complemented by Pt L-2-edge X-ray absorption near-edge spectroscopy (XANES), which probes unoccupied valence states. We found a significant electronic perturbation of the Pt projected d-DOS which was narrowed and shifted to higher binding energy compared to pure platinum. The effect of this electronic structure perturbation on the chemical properties of the nanoparticle surface is discussed in terms of the d-band model. We have thereby demonstrated that the combination of L-edge spectroscopy and HAXPES allows for an experimental derivation of the valence electronic structure in an element-specific way for 5d metal catalysts.

  • 4.
    Arafa, Wael A. A.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Kärkäs, Markus D.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lee, Bao-Lin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Torbjörn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Liao, Rong-Zhen
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Berends, Hans-Martin
    Messinger, Johannes
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Dinuclear manganese complexes for water oxidation: evaluation of electronic effects and catalytic activity2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 24, p. 11950-11964Article in journal (Refereed)
    Abstract [en]

    During recent years significant progress has been made towards the realization of a sustainable and carbon-neutral energy economy. One promising approach is photochemical splitting of H2O into O-2 and solar fuels, such as H-2. However, the bottleneck in such artificial photosynthetic schemes is the H2O oxidation half reaction where more efficient catalysts are required that lower the kinetic barrier for this process. In particular catalysts based on earth-abundant metals are highly attractive compared to catalysts comprised of noble metals. We have now synthesized a library of dinuclear Mn-2 (II,III) catalysts for H2O oxidation and studied how the incorporation of different substituents affected the electronics and catalytic efficiency. It was found that the incorporation of a distal carboxyl group into the ligand scaffold resulted in a catalyst with increased catalytic activity, most likely because of the fact that the distal group is able to promote proton-coupled electron transfer (PCET) from the high-valent Mn species, thus facilitating O-O bond formation.

  • 5. Brinkmann, Andreas
    et al.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Central-transition double-quantum sideband NMR spectroscopy of half-integer quadrupolar nuclei: estimating internuclear distances and probing clusters within multi-spin networks2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 15, p. 7037-7050Article in journal (Refereed)
    Abstract [en]

    We introduce a strategy to estimate the size of clusters of recoupled homonuclear half-integer quadrupolar nuclei under magic-angle spinning (MAS) conditions, by combining double-quantum (2Q) sideband NMR experiments with an approximate numerical analysis based on the summation of all spin-pairs present over a given radius of the structure. The experiment relies solely on the evolution of homonuclear 2Q coherences (2QC) among the central-transitions (CT) of half-integer spins and is suitable for probing clusters in network structures, such as those encountered in large groups of oxide-based materials. Experimental B-11, Na-23 and Al-27 NMR results are presented on bis(catecholato)diboron, Na2SO4 and Al2O3, respectively; in each case, the growth of the spin-cluster size was monitored from a series of experiments that employed progressively lengthened 2QC excitation intervals. Our new approach is the first option for probing larger constellations of half-integer spins; it provides similar information as the multiple-quantum spin counting experiment, which is well-established for spin-1/2 applications but has hitherto not been demonstrated for half-integer spins undergoing MAS. We also discuss various options for determining the internuclear distance within a (nearly) isolated pair of half-integer spins by comparing the experimental 2Q sideband NMR spectra with results from numerical simulations involving various degrees of approximation.

  • 6.
    Cavalleri, M.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nordlund, D.
    Stockholm University, Faculty of Science, Department of Physics.
    Odelius, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, A.
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, L.G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Half or full core hole in density functional theory X-ray absorption spectrum calculations of water?2005In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, no 15, p. 2854-2858Article in journal (Refereed)
    Abstract [en]

    We analyze the performance of two different core-hole potentials in the theoretical modeling of XAS of ice, liquid and gas phase water; the use of a full core-hole (FCH) in the calculations, as suggested by Hetenyi et al. [B. Hetenyi, F. De Angelis, P. Giamozzi and R. Car, J. Chem. Phys., 2004, 120(18), 8632], gives poor agreement with experiment in terms of intensity distribution as well as transition energies, while the half core hole (HCH) potential, in the case of water, provides a better compromise between initial and final state effects, leading to good agreement with the experimental data.

  • 7. Chen, Chen
    et al.
    Huang, Congcong
    Waluyo, Iradwikanari
    Weiss, Thomas
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics. SLAC National Accelerator Laboratory, USA.
    Long-range ion-water and ion-ion interactions in aqueous solutions2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 13, p. 8427-8430Article in journal (Refereed)
    Abstract [en]

    Using small-angle X-ray scattering (SAXS), we obtained direct experimental evidence on the structure of hydrated polyatomic anions, with hydration effects starkly different from those of cations (J. Chem. Phys., 2011, 134, 064513). We propose that the size and charge density of the naked ions do not sufficiently account for the differences in the SAXS curves. For cations, the ion-ion contribution gives a prominent first-order diffraction peak, whereas for anions, the low-Q enhancement in the SAXS curves indicates density inhomogeneities as a result of ion-water interactions.

  • 8. Chen, Shi-Lu
    et al.
    Blomberg, Margareta R. A.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    An investigation of possible competing mechanisms for Ni-containing methyl-coenzyme M reductase2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 27, p. 14029-14035Article in journal (Refereed)
    Abstract [en]

    Ni-containing methyl-coenzyme M reductase (MCR) is capable of catalyzing methane formation from methyl-coenzyme M (CH3-SCoM) and coenzyme B (CoB-SH), and also its reverse reaction (methane oxidation). Based on extensive experimental and theoretical investigations, it has turned out that a mechanism including an organometallic methyl-Ni(III)F-430 intermediate is inaccessible, while another mechanism involving a methyl radical and a Ni(II)-SCoM species currently appears to be the most acceptable one for MCR. In the present paper, using hybrid density functional theory and an active-site model based on the X-ray crystal structure, two other mechanisms were studied and finally also ruled out. One of them, involving proton binding on the CH3-SCoM substrate, which should facilitate methyl-Ni(III)F-430 formation, is demonstrated to be quite unfavorable since the substrate has a much smaller proton affinity than the F-430 cofactor. Another one (oxidative addition mechanism) is also shown to be unfavorable for the MCR reaction, due to the large endothermicity for the formation of the ternary intermediate with side-on C-S (for CH3-SCoM) or C-H (for methane) coordination to Ni.

  • 9.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Uppsala University, Sweden .
    Wardecki, Dariusz
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vasiliev, Petr
    McCusker, Lynne B.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). ETH Zürich, Switzerland.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Highly selective uptake of carbon dioxide on the zeolite vertical bar Na10.2KCs0.8 vertical bar-LTA - a possible sorbent for biogas upgrading2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 24, p. 16080-16083Article in journal (Refereed)
    Abstract [en]

    The vertical bar Na10.2KCs0.8 vertical bar(8)[Al12Si12O48](8)(Fm3c)-LTA zeolite adsorbs CO2-over-CH4 with a high selectivity (over 1500). The uptake of carbon dioxide is also high (3.31 mmol g(-1), 293 K, 101 kPa). This form of zeolite A is a very promising adsorbent for applications such as biogas upgrading, where keeping the adsorption of methane to a minimum is crucial.

  • 10. Dahle, Pal
    et al.
    Helgaker, Trygve
    Jonsson, Dan
    Stockholm University, Faculty of Science, Department of Physics.
    Taylor, Peter R.
    Accurate quantum-chemical calculations using Gaussian-type geminal and Gaussian-type orbital basis sets: applications to atoms and diatomics2007In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 9, no 24, p. 3112-3126Article in journal (Refereed)
    Abstract [en]

    We have implemented the use of mixed basis sets of Gaussian one- and two-electron (geminal) functions for the calculation of second-order Moller-Plesset (MP2) correlation energies. In this paper, we describe some aspects of this implementation, including different forms chosen for the pair functions. Computational results are presented for some closed-shell atoms and diatomics. Our calculations indicate that the method presented is capable of yielding highly accurate second-order correlation energies with rather modest Gaussian orbital basis sets, providing an alternative route to highly accurate wave functions. For the neon atom, the hydrogen molecule, and the hydrogen fluoride molecule, our calculations yield the most accurate MP2 energies published so far. A critical comparison is made with established MP2-R12 methods, revealing an erratic behaviour of some of these methods, even in large basis sets.

  • 11.
    Danilo, Cecile
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Vallet, Valerie
    Flament, Jean-Pierre
    Wahlgren, Ulf
    Stockholm University, Faculty of Science, Department of Physics.
    Effects of the first hydration sphere and the bulk solvent on the spectra of the f(2) isoelectronic actinide compounds: U4+, NpO2+, and PuO22+2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 5, p. 1116-1130Article in journal (Refereed)
    Abstract [en]

    The electronic spectra of the 5f(2) isoelectronic actinide compounds U4+, NpO2+, and PuO22+ have been investigated theoretically both in gas phase and in solution. In the latter case the solvent was modelled by a saturated first hydration sphere, five water molecules for NpO2+, and PuO22+ and eight for U4+, and a continuum model describing the remaining solvent. The transition energies and oscillator strengths were obtained at the spin-orbit level using the relativistic wave function based multi-configuration methods CASPT2 (complete active space with second-order perturbation theory) and MRCI + DC (Davidson corrected multi-reference configuration interaction), followed by a spin-orbit CI based on a dressed effective spin-orbit Hamiltonian. This study is an attempt to contribute to an enhanced understanding of the electronic structure of tetravalent actinide ions and actinyl(V) and (VI) ions. The spin-orbit MRCI and spin-orbit CASPT2 transitions energies have been compared for the bare ions, leading us to the conclusion that the spin-orbit CASPT2 approach is reasonably accurate and can be used with confidence for the calculation of the hydrated species. The first hydration sphere and the bulk solvent lift degeneracies, but the effect on the transition energies is fairly small for the two actinyl ions, while it is larger, up to several thousands of wave numbers for U4+. The calculations allowed us to make assignments of the experimentally observed absorption spectra for all species. The computed transition energies and intensities compared favourably with experiment.

  • 12. Eland, J. H. D.
    et al.
    Fink, R. F.
    Linusson, Per
    Stockholm University, Faculty of Science, Department of Physics.
    Hedin, L.
    Stockholm University, Faculty of Science, Department of Physics.
    Plogmaker, S.
    Stockholm University, Faculty of Science, Department of Physics.
    Feifel, Raimund
    Stockholm University, Faculty of Science, Department of Physics.
    Single and multiple photoionisation of H(2)S by 40-250 eV photons2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 41, p. 18428-18435Article in journal (Refereed)
    Abstract [en]

    Multi-electron coincidence measurements on photoionisation of H(2)S have been carried out at photon energies from 40 to 250 eV. They quantify molecular field effects on the Auger process in detail and are in good agreement with the existing theory. Spectra of core-valence double ionisation of H(2)S are presented and partially analysed. Auger decays from the core-valence states produce triply charged product spectra with unexplained and surprising intensity distributions. Triple ionisation by the double Auger process from 2p hole states shows little effect of the molecular field splitting, but includes a substantial contribution from cascade processes, some involving dissociation in intermediate states. The onset of triple ionisation at the molecular geometry is determined as 61 +/- 0.5 eV.

  • 13. Elm, Jonas
    et al.
    Myllys, Nanna
    Olenius, Tinja
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Halonen, Roope
    Kurtén, Theo
    Vehkamäki, Hanna
    Formation of atmospheric molecular clusters consisting of sulfuric acid and C8H12O6 tricarboxylic acid2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 6, p. 4877-4886Article in journal (Refereed)
    Abstract [en]

    Using computational methods, we investigate the formation of atmospheric clusters consisting of sulfuric acid (SA) and 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA), identified from a-pinene oxidation. The molecular structure of the clusters is obtained using three different DFT functionals (PW91, M06-2X and oB97X-D) with the 6-31++ G(d, p) basis set and the binding energies are calculated using a high level DLPNO-CCSD(T)/ Def2-QZVPP method. The stability of the clusters is evaluated based on the calculated formation free energies. The interaction between MBTCA and sulfuric acid is found to be thermodynamically favourable and clusters consisting of 2-3 MBTCA and 2-3 SA molecules are found to be particularly stable. There is a large stabilization of the cluster when the amount of sulfuric acid-carboxylic acid hydrogen bonded interactions is maximized. The reaction free energies for forming the (MBTCA) 2-3(SA) 2-3 clusters are found to be similar in magnitude to those of the formation of the sulfuric acid-dimethylamine cluster. Using cluster kinetics calculations we identify that the growth of the clusters is essentially limited by a weak formation of the largest clusters studied, implying that other stabilizing vapours are required for stable cluster formation and growth.

  • 14. Eriksson, Susanna K.
    et al.
    Josefsson, Ida
    Stockholm University, Faculty of Science, Department of Physics.
    Ellis, Hanna
    Amat, Anna
    Pastore, Mariachiara
    Oscarsson, Johan
    Lindblad, Rebecka
    Eriksson, Anna I. K.
    Johansson, Erik M. J.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Fantacci, Simona
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Rensmo, Håkan
    Geometrical and energetical structural changes in organic dyes for dye-sensitized solar cells probed using photoelectron spectroscopy and DFT2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 1, p. 252-260Article in journal (Refereed)
    Abstract [en]

    The effects of alkoxy chain length in triarylamine based donor acceptor organic dyes are investigated with respect to the electronic and molecular surface structures on the performance of solar cells and the electron lifetime. The dyes were investigated when adsorbed on TiO2 in a configuration that can be used for dye sensitized solar cells (DSCs). Specifically, the two dyes D35 and D45 were compared using photoelectron spectroscopy (PES) and density functional theory (DFT) calculations. The differences in solar cell characteristics when longer alkoxy chains are introduced in the dye donor unit are attributed to geometrical changes in dye packing while only minor differences were observed in the electronic structure. A higher dye load was observed for D45 on TiO2. However, D35 based solar cells result in higher photocurrent although the dye load is lower. This is explained by different geometrical structures of the dyes on the surface.

  • 15.
    Ermilova, Inna
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Stenberg, Samuel
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Quantum chemical and molecular dynamics modelling of hydroxylated polybrominated diphenyl ethers2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 41, p. 28263-28274Article in journal (Refereed)
    Abstract [en]

    A series of 19 hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have been studied using density functional theory (DFT) and molecular dynamics simulations with the purpose of investigating eventual correlations between their physicochemical properties and toxic action. Dissociation constants (pK(a)), solvation free energies and octanol-water partition coefficients (logP) have been computed. Additionally, metadynamics simulations of OH-PBDEs passing through a lipid bilayer have been carried out for four OH-PBDE species. No correlations between computed pKa values and toxicity data have been found. Medium correlations were found between partition coefficients and the ability of OH-PBDEs to alter membrane potential in cell cultures, which is attributed to higher uptake of molecules with larger log P parameters. It was also demonstrated that in lipid bilayers, OH-PBDE molecules differ in their orientational distributions and can adopt different conformations which can affect the uptake of these molecules and influence the pathways of their toxic action.

  • 16.
    Ertan, Emelie
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Savchenko, Viktoriia
    Ignatova, Nina
    da Cruz, Vinicius Vaz
    Couto, Rafael C.
    Eckert, Sebastian
    Fondell, Mattis
    Dantz, Marcus
    Kennedy, Brian
    Schmitt, Thorsten
    Pietzsch, Annette
    Foelisch, Alexander
    Gel'mukhanov, Faris
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Kimberg, Victor
    Ultrafast dissociation features in RIXS spectra of the water molecule2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 21, p. 14384-14397Article in journal (Refereed)
    Abstract [en]

    In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X-ray scattering (RIXS) spectra of gas phase water via the lowest dissociative core-excited state |1s-1O4a11. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic-like peak consists of the overlapping contribution from the RIXS channels back to the ground state and to the first valence excited state |1b-114a11 of the molecule. The spectral feature has signatures of ultrafast dissociation (UFD) in the core-excited state, as we show by means of ab initio calculations and time-dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic-like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core-excited state resonance, we can understand and single out the molecular and atomic-like contributions in the decay to the lowest valence-excited state. Our study is complemented by a theoretical discussion of RIXS in the case of isotopically substituted water (HDO and D2O) where the nuclear dynamics is significantly affected by the heavier fragments' mass.

  • 17. Fransson, Thomas
    et al.
    Zhovtobriukh, Iurii
    Stockholm University, Faculty of Science, Department of Physics.
    Coriani, Sonia
    Wikfeldt, Kjartan T.
    Stockholm University, Faculty of Science, Department of Physics. University of Iceland, Iceland .
    Norman, Patrick
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Requirements of first-principles calculations of X-ray absorption spectra of liquid water2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 1, p. 566-583Article in journal (Refereed)
    Abstract [en]

    A computational benchmark study on X-ray absorption spectra of water has been performed by means of transition-potential density functional theory (TP-DFT), damped time-dependent density functional theory (TDDFT), and damped coupled cluster (CC) linear response theory. For liquid water, using TDDFT with a tailored CAM-B3LYP functional and a polarizable embedding, we find that an embedding with over 2000 water molecules is required to fully converge spectral features for individual molecules, but a substantially smaller embedding can be used within averaging schemes. TP-DFT and TDDFT calculations on 100 MD structures demonstrate that TDDFT produces a spectrum with spectral features in good agreement with experiment, while it is more difficult to fully resolve the spectral features in the TP-DFT spectrum. Similar trends were also observed for calculations of bulk ice. In order to further establish the performance of these methods, small water clusters have been considered also at the CC2 and CCSD levels of theory. Issues regarding the basis set requirements for spectrum simulations of liquid water and the determination of gas-phase ionization potentials are also discussed.

  • 18. Friebel, Daniel
    et al.
    Miller, Daniel J.
    O'Grady, Christopher P.
    Anniyev, Toyli
    Bargar, John
    Bergmann, Uwe
    Ogasawara, Hirohito
    Wikfeldt, Kjartan Thor
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    In situ x-ray probing reveals the importance of surface platinum oxide formation in fuel cell catalysis2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 1, p. 262-266Article in journal (Refereed)
    Abstract [en]

    In situ X-ray absorption spectroscopy (XAS) at the Pt L3 edge is a useful probe for Pt–O interactions at polymer electrolyte membrane fuel cell (PEMFC) cathodes. We show that XAS using the high energy resolution fluorescence detection (HERFD) mode, applied to a well-defined monolayer Pt/Rh(111) sample where the bulk penetrating hard X-rays probe only surface Pt atoms, provides a unique sensitivity to structure and chemical bonding at the Pt-electrolyte interface. Ab initio multiple-scattering calculations using the FEFF code and complementary extended X-ray absorption fine structure (EXAFS) results indicate that the commonly observed large increase of the white-line at high electrochemical potentials on PEMFC cathodes originates from platinum oxide formation, whereas previously proposed chemisorbed oxygen-containing species merely give rise to subtle spectral changes.

  • 19.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Delaunay, Rudy
    D'Angelo, Giovanna
    Stockholm University, Faculty of Science, Department of Physics. Universidade do Porto, Portugal; Universidad Autónoma de Madrid, Spain.
    Mika, Arkadiusz
    Kulyk, Kostiantyn
    Stockholm University, Faculty of Science, Department of Physics.
    Domaracka, Alicja
    Rousseau, Patrick
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Huber, Bernd A.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Ion-induced molecular growth in clusters of small hydrocarbon chains2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 30, p. 19665-19672Article in journal (Refereed)
    Abstract [en]

    We report on studies of collisions between 3 keV Ar+ projectile ions and neutral targets of isolated 1,3-butadiene (C4H6) molecules and cold, loosely bound clusters of these molecules. We identify molecular growth processes within the molecular clusters that appears to be driven by knockout processes and that could result in the formation of (aromatic) ring structures. These types of reactions are not unique to specific projectile ions and target molecules, but will occur whenever atoms or ions with suitable masses and kinetic energies collide with aggregates of matter, such as carbonaceous grains in the interstellar medium or aerosol nanoparticles in the atmosphere.

  • 20.
    Gatchell, Michael
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Goulart, Marcelo
    Kranabetter, Lorenz
    Kuhn, Martin
    Martini, Paul
    Rasul, Bilal
    Scheier, Paul
    Complexes of gold and imidazole formed in helium nanodroplets2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 11, p. 7739-7745Article in journal (Refereed)
    Abstract [en]

    We have studied complexes of gold atoms and imidazole (C3N2H4, abbreviated Im) produced in helium nanodroplets. Following the ionization of the doped droplets we detect a broad range of different Au(m)Im(n)(+) complexes, however we find that for specific values of m certain n are magic and thus particularly abundant. Our density functional theory calculations indicate that these abundant clusters sizes are partially the result of particularly stable complexes, e.g. AuIm(2)(+), and partially due to a transition in fragmentation patterns from the loss of neutral imidazole molecules for large systems to the loss of neutral gold atoms for smaller systems.

  • 21.
    Giacomozzi, Linda
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    de Ruette, Nathalie
    Stockholm University, Faculty of Science, Department of Physics.
    Wolf, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    D'Angelo, Giovanna
    Stockholm University, Faculty of Science, Department of Physics. Universidade do Porto, Portugal; Universidad Autónoma de Madrid, Spain.
    Schmidt, Henning T.
    Stockholm University, Faculty of Science, Department of Physics.
    Cederquist, Henrik
    Stockholm University, Faculty of Science, Department of Physics.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Knockout driven fragmentation of porphyrins2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 30, p. 19750-19755Article in journal (Refereed)
    Abstract [en]

    We have studied collisions between tetraphenylporphyrin cations and He or Ne at center-of-mass energies in the range 50-110 eV. The experimental results were interpreted in view of density functional theory calculations of dissociation energies and classical molecular dynamics simulations of how the molecules respond to the He/Ne impact. We demonstrate that prompt atom knockout strongly contributes to the total destruction cross sections. Such impulse driven processes typically yield highly reactive fragments and are expected to be important for collisions with any molecular system in this collision energy range, but have earlier been very difficult to isolate for biomolecules.

  • 22.
    Golets, Mikhail
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Shimpi, M. R.
    Wang, Y. -L.
    Antzutkin, O. N.
    Glavatskih, S.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stellenbosch University, South Africa.
    Understanding the thermal decomposition mechanism of a halogen-free chelated orthoborate-based ionic liquid: a combined computational and experimental study2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 32, p. 22458-22466Article in journal (Refereed)
    Abstract [en]

    In the last few decades, ionic liquids (ILs) have gained significant attention as lubricants and lubricant additives due to their polar nature, low vapour pressure and tunable physicochemical properties. In this work, quantum chemistry calculations and atomistic Molecular Dynamics (MD) simulations were employed to predict thermal degradation mechanisms of a potential lubricating agent - the tributyloctylphosphonium bis(oxalato) borate ([P-4,P-4,P-4,P-8][BOB]) IL. It was found that the onset of decomposition of the studied IL coincides with a cleavage of the B-O bonds in the [BOB](-) anion. Consequently, a series of chemical reactions of the [P-4,P-4,P-4,P-8](+) cation with the [BOB](-) anion was triggered yielding alkylboranes, alkenes, trialkylphosphines, CO and CO2. Another ionic system, consisting of [P-4,P-4,P-4,P-8][Cl], was also tested for a comparison. Thermogravimetric measurements have shown a higher thermal stability of [P-4,P-4,P-4,P-8][BOB] compared to that of [P-4,P-4,P-4,P-8][Cl] at least at the initial stage of decomposition, in accord with the presented calculations. Quantum chemical frequency calculations also agreed with the experimental Fourier Transform Infrared (FTIR) spectroscopy results.

  • 23. Goulart, Marcelo
    et al.
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria .
    Kranabetter, Lorenz
    Kuhn, Martin
    Martini, Paul
    Gitzl, Norbert
    Rainer, Manuel
    Postler, Johannes
    Scheier, Paul
    Ellis, Andrew M.
    The adsorption of helium atoms on small cationic gold clusters2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 14, p. 9554-9560Article in journal (Refereed)
    Abstract [en]

    Adducts formed between small gold cluster cations and helium atoms are reported for the first time. These binary ions, Aun+Hem, were produced by electron ionization of helium nanodroplets doped with neutral gold clusters and were detected using mass spectrometry. For a given value of n, the distribution of ions as a function of the number of added helium atoms, m, has been recorded. Peaks with anomalously high intensities, corresponding to so-called magic number ions, are identified and interpreted in terms of the geometric structures of the underlying Au-n(+) ions. These features can be accounted for by planar structures for Au-n(+) ions with n <= 7, with the addition of helium having no significant effect on the structures of the underlying gold cluster ions. According to ion mobility studies and some theoretical predictions, a 3-D structure is expected for Au-8(+). However, the findings for Au-8(+) in this work are more consistent with a planar structure.

  • 24. Goulart, Marcelo
    et al.
    Kuhn, Martin
    Rasul, Bilal
    Postler, Johannes
    Gatchell, Michael
    Stockholm University, Faculty of Science, Department of Physics. Universität Innsbruck, Austria.
    Zettergren, Henning
    Stockholm University, Faculty of Science, Department of Physics.
    Scheier, Paul
    Echt, Olof
    The structure of coronene cluster ions inferred from H-2 uptake in the gas phase2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 41, p. 27968-27973Article in journal (Refereed)
    Abstract [en]

    Mass spectra of helium nanodroplets doped with H-2 and coronene feature anomalies in the ion abundance that reveal anomalies in the energetics of adsorption sites. The coronene monomer ion strongly adsorbs up to n = 38 H-2 molecules indicating a commensurate solvation shell that preserves the D-6h symmetry of the substrate. No such feature is seen in the abundance of the coronene dimer through tetramer complexed with H-2; this observation rules out a vertical columnar structure. Instead we see evidence for a columnar structure in which adjacent coronenes are displaced in parallel, forming terraces that offer additional strong adsorption sites. The experimental value for the number of adsorption sites per terrace, approximately six, barely depends on the number of coronene molecules. The displacement estimated from this number exceeds the value reported in several theoretical studies of the bare, neutral coronene dimer.

  • 25.
    Hahlin, Maria
    et al.
    Uppsala universitet.
    Johansson, Erik M J
    Uppsala universitet.
    Plogmaker, Stefan
    Uppsala universitet.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Hagberg, Daniel P
    Sun, Licheng
    KTH, Organisk kemi.
    Siegbahn, Hans
    Uppsala universitet.
    Rensmo, Håkan
    Uppsala universitet.
    Electronic and molecular structures of organic dye/TiO(2) interfaces for solar cell applications: a core level photoelectron spectroscopy study.2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 7, p. 1507-17Article in journal (Refereed)
    Abstract [en]

    The electronic and molecular properties of three organic dye molecules with the general structure donor-linker-anchor have been investigated using core level photoelectron spectroscopy (PES). The molecules contain a diphenylaniline donor unit, a thiophene linker unit, and cyanoacrylic acid or rhodanine-3-acetic acid anchor units. They have been investigated both in the form of a multilayer and adsorbed onto nanoporous TiO(2) and the experimental results were also compared with DFT calculations. The changes at the dye-sensitized TiO(2) surface due to the modification of either the donor unit or the anchor unit was investigated and the results showed important differences in coverage as well as in electronic and molecular surface properties. By measuring the core level binding energies, the sub-molecular properties were characterized and the result showed that the adsorption to the TiO(2) influences the energy levels of the sub-molecular units differently.

  • 26. Hahlin, Maria
    et al.
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Magnuson, Martin
    Johansson, Erik M. J.
    Plogmaker, Stefan
    Hagberg, Daniel P.
    Sun, Licheng
    Siegbahn, Hans
    Rensmo, Håkan
    Mapping the frontier electronic structures of triphenylamine based organic dyes at TiO2 Interafaces2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, p. 3534--3546Article in journal (Refereed)
    Abstract [en]

    The frontier electronic structures of a series of organic dye molecules containing a triphenylamine moiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental results were compared to electronic structure calculations on the molecules, which are used to confirm and enrich the assignment of the spectra. The approach allows us to experimentally measure and interpret the basic valence energy level structure in the dye, including the highest occupied energy level and how it depends on the interaction between the different units. Based on N 1s X-ray absorption and emission spectra we also obtain insight into the structure of the excited states, the molecular orbital composition and dynamics. Together the results provide an experimentally determined energy level map useful in the design of these types of materials. Included are also results indicating femtosecond charge redistribution at the dye/TiO2 interface.

  • 27. Hansen, Martin Hangaard
    et al.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Rossmeisl, Jan
    Modelling pH and potential in dynamic structures of the water/Pt(111) interface on the atomic scale2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 34, p. 23505-23514Article in journal (Refereed)
    Abstract [en]

    We present atomic-scale structures of the Pt(111)/water interface, by calculating distributions of atomic distances as functions of pH. The structure of the Pt(111)/water interface is a particularly interesting model system in electro-catalysis for proton exchange reactions, especially the oxygen reduction reaction in polymer electrolyte membrane fuel cells. Further insight into such reactions requires accurate simulations of the electrolyte structure in the interface. The study displays many interesting details in the behaviour of the electrolyte structure, e.g. that the electrolyte structure average responds to the presence of protons by a H-down water orientation and that hexagonal adsorbed water layers are present only when they are anchored at the surface by HO*. New adsorbate configurations were also found at 5/12 ML coverage of HO*, suggesting an explanation for reported cyclic voltammetry experiments. The present study is a step towards a more complete understanding of the structure of the electrochemical interface on the atomic scale.

  • 28.
    Holm, Anne I. S.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nielsen, Lisbeth M.
    Kohler, Bern
    Hoffman, Soren Vronning
    Nielsen, Steen Brondsted
    Electronic coupling between cytosine bases in DNA single strands and i-motifs revealed from synchrotron radiation circular dichroism experiments2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 14, p. 3426-3430Article in journal (Refereed)
    Abstract [en]

    In this work we have recorded synchrotron radiation circular dichroism (SRCD) spectra from 180 nm to 360 nm of cytosine strands [(dC)(n), n = 1, 2,..., 10] in aqueous solution at different pH values to reveal electronic coupling between bases in different ionisation states. The geometry of the strands is determined by the pH value and the strand length and the local organisation of the cytosines will determine the base-to-base interaction that impacts on the CD signal. At low pH where all bases are protonated, there is no signature of electronic coupling between the bases, and the SRCD spectrum is simply n times that of the n = 1 spectrum. At higher pH where all bases are neutral, the spectra for n > 1 differ from the monomer spectrum, which implies electronic coupling between bases. The correlation between the CD signal and n is linear, and the spatial extent of the excited state wavefunction is therefore over just two stacked bases both in the UV and VUV. At intermediate pH, the low-n spectra are different from the high-n spectra, and a transition is seen to occur at n = 6-8. We ascribe this behavior to the formation of i-motif structures between four (dC)(n) strands for high n.

  • 29.
    Holm, Anne Ivalu Sander
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Nielsen, Lisbeth Munksgaard
    Hoffmann, Søren Vrønning
    Nielsen, Steen Brøndsted
    Vacuum-ultraviolet circular dichroism spectroscopy of DNA: a valuable tool to elucidate topology and electronic coupling in DNA2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 33, p. 9581-9596Article in journal (Refereed)
    Abstract [en]

    Circular dichroism (CD) is a powerful technique to obtain information on electronic transitions and has been used extensively for studies on DNA. Most experiments are done in the UV region but new information is often revealed from extending the wavelength region down into the vacuum ultraviolet (VUV) region. Such experiments are most easily carried out with synchrotron radiation (SR) light sources that provide large photon fluxes. Here we provide a summary of the SRCD data taken on different DNA strands with emphasis on results from our own laboratory within the last five years.(1-3) Signal intensities in the VUV are often significantly larger than those in the UV, and the electronic coupling between bases may increase with excitation energy. CD spectroscopy is particularly useful for investigating the extent of electronic coupling within a strand, i.e., the degree of delocalisation of the excited-state electronic wavefunction. The spatial extent of the wavefunction may be limited to just one base or it extends over two or more bases in a stack or between bases on different strands.(4,5) The actual character of the electronically excited state is linked to base composition and sequence as well as DNA folding motif (A-, B-, Z-DNA, triplexes, quadruplexes, etc.). The latter depends on experimental conditions such as solution acidity, temperature, ionic strength, and solvent.

  • 30. Huang, Congcong
    et al.
    Wikfeldt, Thor Kjartan
    Stockholm University, Faculty of Science, Department of Physics.
    Nordlund, D.
    Bergmann, U.
    McQueen, T.
    Sellberg, Jonas
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G.M.
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Wide-angle X-ray diffraction and molecular dynamics study of medium-range order in ambient and hot water2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 44, p. 19997-20007Article in journal (Refereed)
    Abstract [en]

    We have developed wide-angle X-ray diffraction measurements with high energy-resolution and accuracy to study water structure at three different temperatures (7, 25 and 66 degrees C) under normal pressure. Using a spherically curved Ge crystal an energy resolution better than 15 eV has been achieved which eliminates influence from Compton scattering. The high quality of the data allows for a reliable Fourier transform of the experimental data resolving shell structure out to similar to 12 angstrom, i.e. 5 hydration shells. Large-scale molecular dynamics (MD) simulations using the TIP4P/2005 force-field reproduce excellently the experimental shell-structure in the range 4-12 angstrom although less agreement is seen for the first peak in the intermolecular pair-correlation function (PCF). The Shiratani-Sasai Local Structure Index [J. Chem. Phys. 104, 7671 (1996)] identifies a tetrahedral minority giving the intermediate-range oscillations in the O-O PCF and a disordered majority providing a more featureless background in this range. The current study supports the proposal that the structure of liquid water, even at high temperatures, can be described in terms of a two-state fluctuation model involving local structures related to the high-density and low-density forms of liquid water postulated in the liquid-liquid phase transition hypothesis.

  • 31. Huse, Nils
    et al.
    Wen, Haidan
    Nordlund, Dennis
    Szilagyi, Erzsi
    Daranciang, Dan
    Miller, Timothy A.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Schoenlein, Robert W.
    Lindenberg, Aaron M.
    Probing the hydrogen-bond network of water via time-resolved soft X-ray spectroscopy2009In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, no 20, p. 3951-3957Article in journal (Refereed)
    Abstract [en]

    We report time-resolved studies of hydrogen bonding in liquid H2O, in response to direct excitation of the O-H stretch mode at 3 mm, probed via soft X-ray absorption spectroscopy at the oxygen K-edge. This approach employs a newly developed nanofluidic cell for transient soft X-ray spectroscopy in the liquid phase. Distinct changes in the near-edge spectral region (XANES) are observed, and are indicative of a transient temperature rise of 10 K following transient laser excitation and rapid thermalization of vibrational energy. The rapid heating occurs at constant volume and the associated increase in internal pressure, estimated to be 8 MPa, is manifested by distinct spectral changes that differ from those induced by temperature alone. We conclude that the near-edge spectral shape of the oxygen K-edge is a sensitive probe of internal pressure, opening new possibilities for testing the validity of water models and providing new insight into the nature of hydrogen bonding in water.

  • 32. Jain, Kalpna
    et al.
    Kaniyankandy, Sreejith
    Kishor, Shyam
    Josefsson, Ida
    Stockholm University, Faculty of Science, Department of Physics.
    Ghosh, Hirendra N.
    Singh, Khundrakpam S.
    Mookerjee, Sumit
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Ramaniah, Lavanya M.
    Density functional investigation and some optical experiments on dye-sensitized quantum dots2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 43, p. 28683-28696Article in journal (Refereed)
    Abstract [en]

    Dye-sensitized quantum dots (QDs) are promising candidates for dye-sensitized solar cells (DSSCs). Here, we report steady state (absorption and photoluminescence) optical measurements on several sizes of CdS QDs ligated with Coumarin 343 dye (C-343) and two different solvents, viz., chloroform and toluene. We further report detailed first principles density functional theory and time-dependent density functional theory studies of the geometric, electronic and optical (absorption and emission) properties of three different sized capped QDs, ligated with C-343 dye. The absorption spectrum shows a QD-size-independent peak, and another peak which shifts to blue with decrease in QD size. The first peak is found to arise from the dye molecule and the second one from the QD. Charge transfer using natural transition orbitals (NTOs) is found to occur from dye-to-QDs and is solvent-dependent. In the emission spectra, the luminescence intensity of the dye is quenched by the addition of the QD indicating a strong interaction between the QD and the dye.

  • 33. Jain, Sandeep K.
    et al.
    Juricic, Vladimir
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Barkema, Gerard T.
    Probing the shape of a graphene nanobubble2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 11, p. 7465-7470Article in journal (Refereed)
    Abstract [en]

    Gas molecules trapped between graphene and various substrates in the form of bubbles are observed experimentally. The study of these bubbles is useful in determining the elastic and mechanical properties of graphene and adhesion energy between graphene and the substrate, and manipulating the electronic properties via strain engineering. In our numerical simulations, we use a simple description of the elastic potential and adhesion energy to show that for small gas bubbles (similar to 10 nm) the van derWaals pressure is in the order of 1 GPa. These bubbles show universal shape behavior irrespective of their size, as observed in recent experiments. With our results, the shape and volume of the trapped gas can be determined via the vibrational density of states (VDOS) using experimental techniques such as inelastic electron tunneling and inelastic neutron scattering. The elastic energy distribution in the graphene layer which traps the nanobubble is homogeneous apart from its edge, but the strain depends on the bubble size; thus variation in bubble size allows control of the electronic and optical properties.

  • 34.
    Jaworski, Aleksander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Edén, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Direct O-17 NMR experimental evidence for Al-NBO bonds in Si-rich and highly polymerized aluminosilicate glasses2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 28, p. 18269-18272Article in journal (Refereed)
    Abstract [en]

    By using solid-state O-17 NMR spectroscopy, we provide the first direct experimental evidence for bonds between Al and non-bridging oxygen (NBO) ions in aluminosilicate glasses based on rare-earth (RE) elements, where RE = {Lu, Sc, Y}. The presence of similar to 10% Al-NBO moieties out of all NBO species holds regardless of the precise glass composition, at odds with the conventional structural view that Al-NBO bonds are absent in highly polymerized and Si-rich aluminosilicate glass networks.

  • 35.
    Jaworski, Aleksander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Pahari, Bholanath
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Okhotnikov, Kirill
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Local structures and al/si ordering in lanthanum aluminosilicate glasses explored by advanced al 27 nmr experiments and molecular dynamics simulations2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 45, p. 15866-15878Article in journal (Refereed)
    Abstract [en]

    The structures of 15 La-Al-Si-O glasses, whose compositions span 11-28 mol% La2O3, 11-30 mol% Al2O3, and 45-78 mol% SiO2, are explored over both short and intermediate length-scales by using a combination of solid-state Al-27 magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulations. MAS NMR reveals Al speciations dominated by AlO4 groups, with minor but significant fractions of AlO5 (5-10%) and AlO6 (less than or similar to 3%) polyhedra present in all La2O3-Al2O3-SiO2 glasses; the amounts of Al-[5] and Al-[6] coordinations increase for decreasing molar fraction of Si. The MD simulations reproduce this compositional trend, with the fractional populations of AlOp groups (p = 4, 5, 6) according well with the experimental results. The modeled La speciations mainly involve LaO6 and LaO7 polyhedra, giving a range of average La3+ coordination numbers between 6.0 and 6.6; the latter increases slightly for decreasing Si content of the sample. Besides the expected bridging and non-bridging O species, minor contributions of oxygen triclusters (<= 9%) and free O-2(-) ions (<= 4%) are observed in all MD data. The glass structures exhibit a pronounced Al/Si disorder; the MD simulations reveal essentially random SiO4-SiO4, SiO4-AlOp and AlOp-AlOq (p, q = 4, 5, 6) associations, including significant amounts of AlO4-AlO4 contacts, regardless of the n(Al)/n(Si) molar ratio of the glass. The strong violation of Al-[4]-Al-[4] avoidance is verified by 2D Al-27 NMR experimentation that correlates double-quantum and single-quantum coherences, here applied for the first time to aluminosilicate glasses, and evidencing AlOp-AlOq connectivities dominated by AlO4-AlO4 and AlO4-AlO5 pairs. The potential bearings from distinct fictive temperatures of the experimental and modeled glass structures are discussed.

  • 36.
    Josefsson, Ida
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Eriksson, Susanna K.
    Ottosson, Niklas
    Ohrwall, Gunnar
    Siegbahn, Hans
    Hagfeldt, Anders
    Rensmo, Håkan
    Björneholm, Olle
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Collective hydrogen-bond dynamics dictates the electronic structure of aqueous I-3(-)2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 46, p. 20189-20196Article in journal (Refereed)
    Abstract [en]

    The molecular and electronic structures of aqueous I-3 and I ions have been investigated through ab initio molecular dynamics (MD) simulations and photoelectron (PE) spectroscopy of the iodine 4d core levels. Against the background of the theoretical simulations, data from our I4d PE measurements are shown to contain evidence of coupled solute-solvent dynamics. The MD simulations reveal large amplitude fluctuations in the I-I distances, which couple to the collective rearrangement of the hydrogen bonding network around the I-3(-) ion. Due to the high polarizability of the I-3(-) ion, the asymmetric I-I vibration reaches partially dissociated configurations, for which the electronic structure resembles that of I-2 + I-. The charge localization in the I-3(-) ion is found to be moderated by hydrogen-bonding. As seen in the PE spectrum, these soft molecular vibrations are important for the electronic properties of the I-3(-) ion in solution and may play an important role in its electrochemical function.

  • 37.
    Jämbeck, Joakim P. M.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Implicit inclusion of atomic polarization in modeling of partitioning between water and lipid bilayers2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 13, p. 4677-4686Article in journal (Refereed)
    Abstract [en]

    We propose an effective and straightforward way of including atomic polarization in simulations of the partitioning of small molecules in inhomogenous media based on classical molecular dynamics with non-polarizable force fields. The approach presented here takes advantage of the relatively fast sampling of phase space obtained with additive force fields by adding the polarization effects afterwards. By using pre-polarized charges for the polar and non-polar phases together with a polarization correction term the effects of atomic polarization are effectively taken into account. The results show a clear improvement compared to using the more common setup with one set of charges obtained from gas phase ab initio calculations. It is shown that when proper measures are taken into account computer simulations with non-polarizable force fields are able to accurately determine water-membrane partitioning and preferential location of small molecules in the membrane interior. We believe that the approach presented here can be useful in rational drug design and in investigations of molecular mechanisms of anesthetic or toxic action.

  • 38.
    Kamerlin, Shina C. L.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Warshel, Arieh
    Multiscale modeling of biological functions2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 22, p. 10401-10411Article in journal (Refereed)
    Abstract [en]

    Recent years have witnessed a tremendous explosion in computational power, which in turn has resulted in great progress in the complexity of the biological and chemical problems that can be addressed by means of all-atom simulations. Despite this, however, our computational time is not infinite, and in fact many of the key problems of the field were resolved long before the existence of the current levels of computational power. This review will start by presenting a brief historical overview of the use of multiscale simulations in biology, and then present some key developments in the field, highlighting several cases where the use of a physically sound simplification is clearly superior to a brute-force approach. Finally, some potential future directions will be discussed.

  • 39.
    Kapla, Jon
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Engström, Olof
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Stevensson, Baltzar
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Wohlert, Jakob
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Maliniak, Arnold
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Molecular dynamics simulations and NMR spectroscopy studies of trehalose-lipid bilayer systems2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 34, p. 22438-22447Article in journal (Refereed)
    Abstract [en]

    The disaccharide trehalose (TRH) strongly affects the physical properties of lipid bilayers. We investigate interactions between lipid membranes formed by 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and TRH using NMR spectroscopy and molecular dynamics (MD) computer simulations. We compare dipolar couplings derived from DMPC/TRH trajectories with those determined (i) experimentally in TRH using conventional high-resolution NMR in a weakly ordered solvent (bicelles), and (ii) by solid-state NMR in multilamellar vesicles (MLV) formed by DMPC. Analysis of the experimental and MD-derived couplings in DMPC indicated that the force field used in the simulations reasonably well describes the experimental results with the exception for the glycerol fragment that exhibits significant deviations. The signs of dipolar couplings, not available from the experiments on highly ordered systems, were determined from the trajectory analysis. The crucial step in the analysis of residual dipolar couplings (RDCs) in TRH determined in a bicelle-environment was access to the conformational distributions derived from the MD trajectory. Furthermore, the conformational behavior of TRH, investigated by J-couplings, in the ordered and isotropic phases is essentially identical, indicating that the general assumptions in the analyses of RDCs are well founded.

  • 40. Kjaer, Christina
    et al.
    Brøndsted Nielsen, Steen
    Stockett, Mark H.
    Stockholm University, Faculty of Science, Department of Physics.
    Sibling rivalry: intrinsic luminescence from two xanthene dye monoanions, resorufin and fluorescein, provides evidence for excited-state proton transfer in the latter2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 36, p. 24440-24444Article in journal (Refereed)
    Abstract [en]

    While the emission spectrum of fluorescein monoanions isolated in vacuo displays a broad and featureless band, that of resorufin, also belonging to the xanthene family, has a sharp band maximum, clear vibronic structure, and experiences a small Stokes shift. Excitedstate proton transfer in fluorescein can account for the differences.

  • 41. Li, Cui
    et al.
    Salén, Peter
    Stockholm University, Faculty of Science, Department of Physics.
    Yatsyna, Vasyl
    Schio, Luca
    Feifel, Raimund
    Squibb, Richard
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics. Jan Kochanowski University, Poland.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Richter, Robert
    Alagia, Michele
    Stranges, Stefano
    Monti, Susanna
    Carravetta, Vincenzo
    Zhaunerchyk, Vitali
    Experimental and theoretical XPS and NEXAFS studies of N-methylacetamide and N-methyltrifluoroacetamide2016In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 3, p. 2210-2218Article in journal (Refereed)
    Abstract [en]

    Experimental Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectra of N-methyltrifluoroacetamide (FNMA), which is a peptide model system, measured at the C, N, O and F K-edges are reported. The features in the spectra have been assigned by Static-Exchange (STEX) calculations. Using the same method, we have also assigned previously measured NEXAFS spectra of another peptide model system, N-methylacetamide (NMA). To facilitate the NEXAFS feature assignments, X-ray Photoelectron Spectroscopy (XPS) measurements for NMA and FNMA have been carried out with the aim of obtaining the 1s electron ionization potentials, which are compared with the values predicted by our Hartree-Fock (Delta HF) and Multi Configuration Self Consistent Field (Delta MCSCF) calculations. We also demonstrate an approach to compensate for screening effects that are neglected in the STEX method. Ion yield measurements of FNMA associated with the excitation of several C, N, O, and F K-shell pre-edge resonances have revealed site-specific fragmentation in some cases which we interpret with the aid of our theoretical calculations.

  • 42.
    Li, Xichen
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Beijing Normal University, People's Republic of China.
    Siegbahn, Per E. M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Alternative mechanisms for O-2 release and O-O bond formation in the oxygen evolving complex of photosystem II2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 18, p. 12168-12174Article in journal (Refereed)
    Abstract [en]

    In a previous detailed study of all the steps of water oxidation in photosystem II, it was surprisingly found that O-2 release is as critical for the rate as O-O bond formation. A new mechanism for O-2 release has now been found, which can be described as an opening followed by a closing of the interior of the oxygen evolving complex. A transition state for peroxide rotation forming a superoxide radical, missed in the previous study, and a structural change around the outside manganese are two key steps in the new mechanism. However, O-2 release may still remain rate-limiting. Additionally, for the step forming the O-O bond, an alternative, experimentally suggested, mechanism was investigated. The new model calculations can rule out the precise use of that mechanism. However, a variant with a rotation of the ligands around the outer manganese by about 301 will give a low barrier, competitive with the old DFT mechanism. Both these mechanisms use an oxyl-oxo mechanism for O-O bond formation involving the same two manganese atoms and the central oxo group (O5).

  • 43. Lindgren, Matteus
    et al.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Westlund, Per-Olof
    A theoretical spin relaxation and molecular dynamics simulation study of the Gd(H2O)(9)(3+) complex2009In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 11, no 44, p. 10368-10376Article in journal (Refereed)
    Abstract [en]

    A theoretical analysis of the paramagnetically enhanced water proton spin-lattice relaxation of a hydrated Gd3+ ion is combined with  Molecular Dynamics (MD) simulations. The electron-proton dipole-dipole  correlation function, C-p(DD)(tau), as well as the pseudo-rotation ( PR) model of the transient zero-field splitting (ZFS) are evaluated  with the help of the data from MD simulations. The fast local water  motion in the first hydration shell, i.e. the wagging and rocking motions, is found not to change the mono exponential character of the dipole correlation function C-p(DD)(tau), but is important in the time dependence of the transient ZFS interaction. The dynamics of the transient ZFS interaction is modeled as the water-induced electric field gradient tensor at the site of the metal ion. This approach follows the ideas of the pseudo-rotation model, describing the fluctuating zero-field interaction as a constant amplitude in the principal frame but reorienting according to a rotational diffusion equation of motion. The MD results indicate that the pseudo-rotation model gives a multi-exponential correlation function which oscillates at short times and is described by three exponential terms. The time scale is shorter than previously assumed but contain an intermediate time constant (1-2 ps). The electron spin resonance (ESR) spectral width at half height at frequencies of X- band,Q-band, 75 MHz, 150 MHz and 225 MHz can be reproduced at 320 K  without any contributions from 4th or 6th rank ZFS interactions. Consequently,there are two mutually inconsistent dynamic models of the  ZFS interaction which can describe the water proton T-1-NMRD (nuclear  magnetic resonance dispersion) profile and the field dependent ESR spectra of the hydrated Gd(III) complex equally well.

  • 44.
    Lindén, Carl Fredrik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Žabka, Ján
    Polášek, Miroslav
    Zymakb, Illia
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    The reaction of C5N- with acetylene as a possible intermediate step to produce large anions in Titan’s ionosphere2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 8, p. 5377-5388Article in journal (Refereed)
    Abstract [en]

    A theoretical and experimental investigation of the reaction C5N + C2H2 has been carried out. This reaction is of astrophysical interest since the growth mechanism of large anions that have been detected in Titan's upper atmosphere by the Cassini plasma spectrometer are still largely unknown. The experimental studies have been performed using a tandem quadrupole mass spectrometer which allows identification of the different reaction channels and assessment of their reaction thresholds. Results of these investigations were compared with the predictions of ab initio calculations, which identified possible pathways leading to the observed products and their thermodynamical properties. These computations yielded that the majority of these products are only accessible via energy barriers situated more than 1 eV above the reactant energies. In many cases, the thresholds predicted by the ab initio calculations are in good agreement with the experimentally observed ones. For example, the chain elongation reaction leading to C7N, although being slightly exoergic, possesses an energy barrier of 1.91 eV. Therefore, the title reaction can be regarded to be somewhat unlikely to be responsible for the formation of large anions in cold environments such as interstellar medium or planetary ionospheres.

  • 45.
    Lo, Andy Y. H.
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Eden, Mattias
    Stockholm University, Faculty of Science, Department of Physics.
    Efficient symmetry-based homonuclear dipolar recoupling of quadrupolar spins: double-quantum NMR correlations in amorphous solids2008In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 10, no 44, p. 6635-6644Article in journal (Refereed)
    Abstract [en]

    We report novel symmetry-based pulse sequences for exciting double-quantum (2Q) coherences between the central transitions of half-integer spin quadrupolar nuclei in the NMR of rotating solids. Compared to previous 2Q-recoupling techniques, numerical simulations and Na-23 and Al-27 NMR experiments on Na2SO4 and the open-framework aluminophosphate AlPO-CJ19 verify that the new dipolar recoupling schemes display higher robustness to both radio-frequency field inhomogeneity and to spreads in resonance frequencies. These advances allowed for the first demonstration of 2Q-recoupling in an amorphous solid for revealing its intermediate-range structural features, in the context of mapping Al-27-Al-27 connectivities between the aluminium polyhedra (AlO4, AlO5 and AlO6) of a lanthanum aluminate glass (La0.18Al0.82O1.5).

  • 46.
    Mace, Amber
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laasonen, Kari
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Free energy barriers for CO2 and N-2 in zeolite NaKA: an ab initio molecular dynamics approach2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 1, p. 166-172Article in journal (Refereed)
    Abstract [en]

    Ab initio Molecular Dynamics (AIMD) is used with spatial constraints to estimate the free energy barriers of diffusion for CO2 and N-2 gas molecules in zeolite NaA and KA. We investigate the extent to which the diffusion of these gas molecules is hindered, in the two separate cases of a smaller Na+ ion or a larger K+ ion blocking the 8-ring pore window. In contrast to classical Molecular Dynamics, AIMD performs these computations accurately and unbiased in the absence of empirical parameterization. Our work has resulted in stable and reliable force profiles. The profiles show that the larger K+ ion effectively blocks the passage of both CO2 and N-2 molecules while the smaller Na+ ion will allow both molecules to pass. These results are a quantitative demonstration of the concept of pore blocking where we compute the effect, which the size of the respective cation occupying the pore window has on diffusive properties of each gas molecule. Hence, this effect can be altered through ion exchange to fine-tune the functionality of a specific zeolite as a molecular sieve.

  • 47.
    Mirzoev, Alexander
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Lyubartsev, Alexander P.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Effective solvent mediated potentials of Na+ and Cl ions in aqueous solution: temperature dependence2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, no 13, p. 5722-5727Article in journal (Refereed)
    Abstract [en]

    The effective solvent-mediated potentials for Na+ and Cl ions in aqueous solution were calculated in a wide range of temperatures from 0 to 100 °C. The potentials have been determined using the inverse Monte Carlo approach, from the ion–ion radial distribution functions computed in 50 ns molecular dynamics simulations of ions and explicit water molecules. We further separated the effective potentials into a short-range part and an electrostatic long-range part represented by a coulombic potential with some dielectric permittivity. We adjusted the value of the dielectric permittivity to provide the fastest possible decay of the short-range potentials at larger distances. The obtained temperature dependence of the dielectric permittivity follows well the experimental data. We show also that the largest part of the temperature dependence of the effective potentials can be attributed to the temperature-dependent dielectric permittivity.

  • 48.
    Norell, Jesper
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Jay, Raphael M.
    Hantschmann, Markus
    Eckert, Sebastian
    Guo, Meiyuan
    Gaffney, Kelly J.
    Wernet, Philippe
    Lundberg, Marcus
    Föhlisch, Alexander
    Odelius, Michael
    Stockholm University, Faculty of Science, Department of Physics.
    Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 10, p. 7243-7253Article in journal (Refereed)
    Abstract [en]

    We describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L-3-edge RIXS in the ferricyanide complex Fe(CN)(6)(3-), we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject the presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.

  • 49. Novoa-Carballal, Ramón
    et al.
    Säwén, Elin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Fernandez-Megia, Eduardo
    Correa, Juan
    Riguera, Ricardo
    Widmalm, Göran
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    The dynamics of GATG glycodendrimers by NMR diffusion and quantitative 13C relaxation2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 25, p. 6587-6589Article in journal (Refereed)
    Abstract [en]

    The dynamics of GATG glycodendrimers have been investigated by NMR translational diffusion and quantitative 13C relaxation studies (Lipari-Szabo model-free), allowing the determination of the correlation times describing the dendrimer segmental orientational mobility.

  • 50.
    Nozière, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Dziedzic, Pawel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Inorganic ammonium salts and carbonate salts are efficient catalysts for aldol condensation in atmospheric aerosols2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 15, p. 3864-3872Article in journal (Refereed)
    Abstract [en]

    In natural environments such as atmospheric aerosols, organic compounds coexist with inorganic salts but, until recently, were not thought to interact chemically. We have recently shown that inorganic ammonium ions, NH4+, act as catalysts for acetal formation from glyoxal, a common atmospheric gas. In this work, we report that inorganic ammonium ions, NH4+, and carbonate ions, CO32−, are also efficient catalysts for the aldol condensation of carbonyl compounds. In the case of NH4+ this was not previously known, and was patented prior to this article. The kinetic results presented in this work show that, for the concentrations of ammonium and carbonate ions present in tropospheric aerosols, the aldol condensation of acetaldehyde and acetone could be as fast as in concentrated sulfuric acid and might compete with their reactions with OH radicals. These catalytic processes could produce significant amounts of polyconjugated, light-absorbing compounds in aerosols, and thus affect their direct forcing on climate. For organic gases with large Henry's law coefficients, these reactions could also result in a significant uptake and in the formation of secondary organic aerosols (SOA). This work reinforces the recent findings that inorganic salts are not inert towards organic compounds in aerosols and shows, in particular, that common ones, such as ammonium and carbonate salts, might even play important roles in their chemical transformations.

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