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  • 101.
    Sarman, Sten
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Laaksonen, Aatto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Flow alignment phenomena in liquid crystals studied by molecular dynamics simulation2009Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 14, s. -144904Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The flow alignment of a nematic liquid crystal has been studied as a function of temperature, beginning at high temperature in the nematic phase and down to the nematic-smectic A phase transition. The alignment angle is obtained by estimating the twist viscosities by nonequilibrium molecular dynamics (NEMD) methods. These estimates are cross-checked by evaluating the corresponding equilibrium fluctuation relations. As a further comparison, shear flow simulations are carried out by application of the SLLOD equations of motion (so named because of their close relationship to the Doll's equation of motion, which can be derived from the Doll's tensor Hamiltonian), whereby the alignment angle is obtained directly. All these methods give consistent results for the alignment angle. At low temperatures near the nematic-smectic A transition the system becomes flow unstable. In this region the alignment angle has been calculated as a function of time.

  • 102.
    Sarman, Sten
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Wang, Yong-Lei
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Laaksonen, Aatto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Self-diffusion in the non-Newtonian regime of shearing liquid crystal model systems based on the Gay-Berne potential2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, nr 5, artikkel-id 054901Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The self-diffusion coefficients of nematic phases of various model systems consisting of regular convex calamitic and discotic ellipsoids and non-convex bodies such as bent-core molecules and soft ellipsoid strings have been obtained as functions of the shear rate in a shear flow. Then the self-diffusion coefficient is a second rank tensor with three different diagonal components and two off-diagonal components. These coefficients were found to be determined by a combination of two mechanisms, which previously have been found to govern the self-diffusion of shearing isotropic liquids, namely, (i) shear alignment enhancing the diffusion in the direction parallel to the streamlines and hindering the diffusion in the perpendicular directions and (ii) the distortion of the shell structure in the liquid whereby a molecule more readily can escape from a surrounding shell of nearest neighbors, so that the mobility increases in every direction. Thus, the diffusion parallel to the streamlines always increases with the shear rate since these mechanisms cooperate in this direction. In the perpendicular directions, these mechanisms counteract each other so that the behaviour becomes less regular. In the case of the nematic phases of the calamitic and discotic ellipsoids and of the bent core molecules, mechanism (ii) prevails so that the diffusion coefficients increase. However, the diffusion coefficients of the soft ellipsoid strings decrease in the direction of the velocity gradient because the broadsides of these molecules are oriented perpendicularly to this direction due the shear alignment (i). The cross coupling coefficient relating a gradient of tracer particles in the direction of the velocity gradient and their flow in the direction of the streamlines is negative and rather large, whereas the other coupling coefficient relating a gradient in the direction of the streamlines and a flow in the direction of the velocity gradient is very small.

  • 103. Savee, John D.
    et al.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mann, Jennifer E.
    Continetti, Robert E.
    Dissociative charge exchange dynamics of HN2+ and DN2+2009Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 13, s. 134301-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Translational spectroscopy coupled with coincidence detection techniques has been used to study the dissociation dynamics of ground state H/D+N-2 products resulting from charge exchange between keV beams of HN2+/DN2+ and cesium. Analysis of the product kinetic energy release suggests that dissociation of HN2 and DN2 proceeds from initial populations in the (2)A '', 2 (2)A ', and 3s Rydberg electronic states of the neutral molecule. Although all three excited electronic states must eventually couple to the 1 (2)A ' ground state of HN2/DN2, the resulting dissociation dynamics exhibit a significant dependence on the initial electronic state. Potential mechanisms are discussed in light of the observed product kinetic energy release distributions.

  • 104.
    Schalk, Oliver
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Geng, Ting
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hansson, Tony
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    The ring-opening channel and the influence of Rydberg states on the excited state dynamics of furan and its derivatives2018Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, nr 8, artikkel-id 084303Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One important relaxation pathway for photo-excited five-membered heterocyclic organic molecules is ring-opening via a dissociative pi sigma* state. In this study, we investigate the influence of this pathway in furan and several hydrogenated and methylated derivatives by combining time-resolved photoelectron spectroscopy with time-dependent density functional theory and coupled cluster calculations. We find strong experimental evidence that the ring-opening channel is the major relaxation channel in furan, 2,3-dihydrofuran, and 2-methylfuran (2-MF). In 2,5-dimethylfuran (25-DMF), however, we observe that the molecules relax either via a pi 3s Rydberg state or through a direct return to the ground state by undergoing ring-puckering motions. From the supporting calculations, for 2-MF and 25-DMF, we predict that there is strong mixing between the pi sigma* state and the pi 3s Rydberg state along the ring opening pathway. However, in 25-DMF, no crossing between the pi sigma*/pi 3s state and the initially excited pi pi* state can be found along the ring opening coordinate, effectively blocking this channel.

  • 105.
    Schalk, Oliver
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Josefsson, Ida
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Geng, Ting
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Richter, Robert
    Sa'adeh, Hanan
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mucke, Melanie
    Dissociation kinetics of excited ions: PEPICO measurements of Os-3(CO)(12) - The 7-35 eV single ionization binding energy region2018Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, nr 8, artikkel-id 084301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this article, we study the photoinduced dissociation pathways of a metallocarbonyl, Os-3(CO)(12), in particular the consecutive loss of CO groups. To do so, we performed photoelectron-photoion coincidence (PEPICO) measurements in the single ionization binding energy region from 7 to 35 eV using 45-eV photons. Zero-energy ion appearance energies for the dissociation steps were extracted by modeling the PEPICO data using the statistical adiabatic channel model. Upon ionization to the excited ionic states above 13 eV binding energy, non-statistical behaviorwas observed and assigned to prompt CO loss. Double ionization was found to be dominated by the knockout process with an onset of 20.9 similar to 0.4 eV. The oscillator strength is significantly larger for energies above 26.6 similar to 0.4 eV, corresponding to one electron being ejected from the Os3 center and one from the CO ligands. The cross section for double ionization was found to increase linearly up to 35 eV ionization energy, at which 40% of the generated ions are doubly charged.

  • 106.
    Schalk, Oliver
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Josefsson, Ida
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Richter, Robert
    Prince, Kevin C.
    Odelius, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mucke, Melanie
    Ionization and photofragmentation of Ru-3(CO)(12) and Os-3(CO)(12)2015Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 143, nr 15, artikkel-id 154305Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, we use a combination of photoelectron spectroscopy, mass spectrometry, and density functional theory calculations to get a detailed understanding of valence single and double ionization and the subsequent dissociation processes. This is exemplified on benchmark systems, trimetallo-dodecacarbonyls M-3(CO)(12) with M = Ru, Os, where the energy remaining in the molecule after photoionization can be retrieved by measuring the degree of fragmentation of the molecular ion. The intensity of different mass peaks can thus be directly related to ionization cross sections obtained by photoelectron spectroscopy. We find that the M-CO dissociation energy rises as the number of CO ligands decreases due to dissociation. Moreover, ionization of the CO ligands has a higher cross section than that of the metal center for both single and double ionization. After advanced fragmentation, a CO bond can break and the carbon atom remains bonded to the metal core. In addition, we found that the valence ionization cross sections of M-3(CO)(12) are maximal at about 40 eV photon energy thus showing a more pronounced shape resonance than Ru and Os-complexes with a single metal atom center. Finally, an np. nd giant resonance absorption causes a significant increase of the ionization cross section above 50 eV for Ru-3(CO)(12).

  • 107.
    Schiros, Theanne
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory .
    Andersson, K. J.
    MacNaughton, J.
    Gladh, Jörgen
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Matsuda, Akitaka
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Nagoya University .
    Östrom, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Takahashi, O.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory .
    Ogasawara, H.
    Unique water-water coordination tailored by a metal surface2013Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, nr 23, s. 234708-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    At low coverage of water on Cu(110), substrate-mediated electrostatics lead to zigzagging chains along [001] as observed with STM [T. Yamada, S. Tamamori, H. Okuyama, and T. Aruga, Anisotropic water chain growth on Cu(110) observed with scanning tunneling microscopy Phys. Rev. Lett. 96, 036105 (2006)]. Using x-ray absorption spectroscopy we find an anomalous low-energy resonance at similar to 533.1 eV which, based on density functional theory spectrum simulations, we assign to an unexpected configuration of water units whose uncoordinated O-H bonds directly face those of their neighbors; this interaction repeats over trough sites with enhanced electron density and is analogous to the case of a hydrated electron.

  • 108.
    Schiros, Theanne
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Takahashi, Osamu
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Andersson, Klas J.
    Haldor-Topsoe.
    Öström, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pettersson, Lars G.M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ogasawara, Hirohito
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    The Role of Substrate Electrons in the Wetting of a Metal Surface2010Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, nr 9, s. 094701-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We address how the electronic and geometric structures of metal surfaces determine water-metal bonding by affecting the balance between Pauli repulsion and electrostatic attraction. We show how the rigid d-electrons and the softer s-electrons utilize different mechanisms for the redistribution of charge that enables surface wetting. On open d-shell Pt(111), the ligand field of water alters the distribution of metal d-electrons to reduce the repulsion. The closed-shell Cu d10 configuration of isostructural Cu(111), however, does not afford this mechanism, resulting in a hydrophobic surface and three-dimensional ice cluster formation. On the geometrically corrugated Cu(110) surface, however, charge depletion involving the mobile sp-electrons at atomic rows reduces the exchange repulsion sufficiently such that formation of a two-dimensional wetting layer is still favored in spite of the d10 electronic configuration

  • 109.
    Schlesinger, Daniel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Sellberg, Jonas A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Evaporative cooling of microscopic water droplets in vacuo: Molecular dynamics simulations and kinetic gas theory2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, nr 12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present study, we investigate the process of evaporative cooling of nanometer-sized droplets in vacuum using molecular dynamics simulations with the TIP4P/2005 water model. The results are compared to the temperature evolution calculated from the Knudsen theory of evaporation which is derived from kinetic gas theory. The calculated and simulation results are found to be in very good agreement for an evaporation coefficient equal to unity. Our results are of interest to experiments utilizing droplet dispensers as well as to cloud micro-physics.

  • 110.
    Schlesinger, Daniel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Wikfeldt, K. Thor
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Skinner, Lawrie B.
    Benmore, Chris J.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    The temperature dependence of intermediate range oxygen-oxygen correlations in liquid water2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, nr 8, artikkel-id 084503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We analyze the recent temperature dependent oxygen-oxygen pair-distribution functions from experimental high-precision x-ray diffraction data of bulk water by Skinner et al. [J. Chem. Phys. 141, 214507 (2014)] with particular focus on the intermediate range where small, but significant, correlations are found out to 17 angstrom. The second peak in the pair-distribution function at 4.5 angstrom is connected to tetrahedral coordination and was shown by Skinner et al. to change behavior with temperature below the temperature of minimum isothermal compressibility. Here we show that this is associated also with a peak growing at 11 angstrom which strongly indicates a collective character of fluctuations leading to the enhanced compressibility at lower temperatures. We note that the peak at similar to 13.2 angstrom exhibits a temperature dependence similar to that of the density with a maximum close to 277 K or 4 degrees C. We analyze simulations of the TIP4P/2005 water model in the same manner and find excellent agreement between simulations and experiment albeit with a temperature shift of similar to 20 K.

  • 111.
    Schreck, Simon
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Diesen, Elias
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    LaRue, Jerry
    Ogasawara, Hirohito
    Marks, Kess
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nordlund, Dennis
    Weston, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Beye, Martin
    Cavalca, Filippo
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Perakis, Fivos
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Sellberg, Jonas
    Eilert, André
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kim, Kyung Hwan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Coslovich, Giacomo
    Coffee, Ryan
    Krzywinski, Jacek
    Reid, Alex
    Moeller, Stefan
    Lutman, Alberto
    Öström, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Atom-specific activation in CO oxidation2018Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, nr 23, artikkel-id 234707Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on atom-specific activation of CO oxidation on Ru(0001) via resonant X-ray excitation. We show that resonant 1s core-level excitation of atomically adsorbed oxygen in the co-adsorbed phase of CO and oxygen directly drives CO oxidation. We separate this direct resonant channel from indirectly driven oxidation via X-ray induced substrate heating. Based on density functional theory calculations, we identify the valence-excited state created by the Auger decay as the driving electronic state for direct CO oxidation. We utilized the fresh-slice multi-pulse mode at the Linac Coherent Light Source that provided time-overlapped and 30 fs delayed pairs of soft X-ray pulses and discuss the prospects of femtosecond X-ray pump X-ray spectroscopy probe, as well as X-ray two-pulse correlation measurements for fundamental investigations of chemical reactions via selective X-ray excitation.

  • 112.
    Seitz, Fabian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Holm, Anne I. S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Johansson, Henrik A. B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosén, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Lawicki, A.
    Rangama, J.
    Rousseau, P.
    Capron, M.
    Maisonny, R.
    Domaracka, A.
    Adoui, L.
    Mery, A.
    Manil, B.
    Huber, B. A.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Polycyclic aromatic hydrocarbon-isomer fragmentation pathways: Case study for pyrene and fluoranthene molecules and clusters2011Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, nr 6, s. 064302-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on measurements of the ionization and fragmentation of polycyclic aromatic hydrocarbon (PAH) targets in Xe(20+) + C(16)H(10) and Xe(20+) + [C(16)H(10)](k) collisions and compare results for the two C(16)H(10) isomers: pyrene and fluoranthene. For both types of targets, i.e., for single PAH molecules isolated in vacuum or for isomerically pure clusters of one of the molecules, the resulting fragment spectra are surprisingly similar. However, we do observe weak but significant isomer effects. Although these are manifested in very different ways for the monomer and cluster targets, they both have at their roots small differences (<2.5 eV) between the total binding energies of neutral, and singly and multiply charged pyrene and fluoranthene monomers. The results will be discussed in view of the density functional theory calculations of ionization and dissociation energies for fluoranthene and pyrene. A simple classical over-the-barrier model is used to estimate cross sections for single-and multiple-electron transfer between PAHs and ions. Calculated single and multiple ionization energies, and the corresponding model PAH ionization cross sections, are given.

  • 113.
    Seitz, Fabian
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Zettergren, Henning
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rousseau, P.
    Wang, Y.
    Chen, Tao
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gatchell, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Alexander, John D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Stockett, Mark H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rangama, J.
    Chesnel, J. Y.
    Capron, M.
    Poully, J. C.
    Domaracka, A.
    Mery, A.
    Maclot, S.
    Vizcaino, V.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Adoui, L.
    Alcami, M.
    Tielens, A. G. G. M.
    Martin, F.
    Huber, B. A.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ions colliding with clusters of fullerenes-Decay pathways and covalent bond formations2013Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 139, nr 3, artikkel-id 034309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report experimental results for the ionization and fragmentation of weakly bound van der Waals clusters of n C-60 molecules following collisions with Ar2+, He2+, and Xe20+ at laboratory kinetic energies of 13 keV, 22.5 keV, and 300 keV, respectively. Intact singly charged C-60 monomers are the dominant reaction products in all three cases and this is accounted for by means of Monte Carlo calculations of energy transfer processes and a simple Arrhenius-type [C-60](n)(+) -> C-60(+) + (n - 1)C-60 evaporation model. Excitation energies in the range of only similar to 0.7 eV per C-60 molecule in a [C-60](13)(+) cluster are sufficient for complete evaporation and such low energies correspond to ion trajectories far outside the clusters. Still we observe singly and even doubly charged intact cluster ions which stem from even more distant collisions. For penetrating collisions the clusters become multiply charged and some of the individual molecules may be promptly fragmented in direct knock-out processes leading to efficient formations of new covalent systems. For Ar2+ and He2+ collisions, we observe very efficient C-119(+) and C-118(+) formation and molecular dynamics simulations suggest that they are covalent dumb-bell systems due to bonding between C-59(+) or C-58(+) and C-60 during cluster fragmentation. In the Ar2+ case, it is possible to form even smaller C-120-2m(+) molecules (m = 2-7), while no molecular fusion reactions are observed for the present Xe20+ collisions.

  • 114.
    Sellberg, Jonas A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    Kaya, Sarp
    Segtnan, Vegard H.
    Chen, Chen
    Tyliszczak, Tolek
    Ogasawara, Hirohito
    Nordlund, Dennis
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    Comparison of x-ray absorption spectra between water and ice: New ice data with low pre-edge absorption cross-section2014Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 141, nr 3, s. 034507-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of crystal growth conditions on the O K-edge x-ray absorption spectra of ice is investigated through detailed analysis of the spectral features. The amount of ice defects is found to be minimized on hydrophobic surfaces, such as BaF2(111), with low concentration of nucleation centers. This is manifested through a reduction of the absorption cross-section at 535 eV, which is associated with distorted hydrogen bonds. Furthermore, a connection is made between the observed increase in spectral intensity between 544 and 548 eV and high-symmetry points in the electronic band structure, suggesting a more extended hydrogen-bond network as compared to ices prepared differently. The spectral differences for various ice preparations are compared to the temperature dependence of spectra of liquid water upon supercooling. A double-peak feature in the absorption cross-section between 540 and 543 eV is identified as a characteristic of the crystalline phase. The connection to the interpretation of the liquid phase O K-edge x-ray absorption spectrum is extensively discussed.

  • 115.
    Sellberg, Jonas A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    McQueen, Trevor A.
    Laksmono, Hartawan
    Schreck, Simon
    Beye, Martin
    DePonte, Daniel P.
    Kennedy, Brian
    Nordlund, Dennis
    Sierra, Raymond G.
    Schlesinger, Daniel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Tokushima, Takashi
    Zhovtobriukh, Iurii
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Eckert, Sebastian
    Segtnan, Vegard H.
    Ogasawara, Hirohito
    Kubicek, Katharina
    Techert, Simone
    Bergmann, Uwe
    Dakovski, Georgi L.
    Schlotter, William F.
    Harada, Yoshihisa
    Bogan, Michael J.
    Wernet, Philippe
    Foehlisch, Alexander
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    X-ray emission spectroscopy of bulk liquid water in no-man's land2015Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, nr 4, artikkel-id 044505Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The structure of bulk liquid water was recently probed by x-ray scattering below the temperature limit of homogeneous nucleation (T-H) of similar to 232 K [J. A. Sellberg et al., Nature 510, 381-384 (2014)]. Here, we utilize a similar approach to study the structure of bulk liquid water below T-H using oxygen K-edge x-ray emission spectroscopy (XES). Based on previous XES experiments [T. Tokushima et al., Chem. Phys. Lett. 460, 387-400 (2008)] at higher temperatures, we expected the ratio of the 1b(1)' and 1b(1) peaks associated with the lone-pair orbital in water to change strongly upon deep supercooling as the coordination of the hydrogen (H-) bonds becomes tetrahedral. In contrast, we observed only minor changes in the lone-pair spectral region, challenging an interpretation in terms of two interconverting species. A number of alternative hypotheses to explain the results are put forward and discussed. Although the spectra can be explained by various contributions from these hypotheses, we here emphasize the interpretation that the line shape of each component changes dramatically when approaching lower temperatures, where, in particular, the peak assigned to the proposed disordered component would become more symmetrical as vibrational interference becomes more important.

  • 116. Skinner, Lawrie B.
    et al.
    Huang, Congcong
    Schlesinger, Daniel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    Benmore, Chris J.
    Benchmark oxygen-oxygen pair-distribution function of ambient water from x-ray diffraction measurements with a wide Q-range2013Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, nr 7, artikkel-id 074506Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Four recent x-ray diffraction measurements of ambient liquid water are reviewed here. Each of these measurements represents a significant development of the x-ray diffraction technique applied to the study of liquid water. Sources of uncertainty from statistical noise, Q-range, Compton scattering, and self-scattering are discussed. The oxygen-hydrogen contribution to the measured x-ray scattering pattern was subtracted using literature data to yield an experimental determination, with error bars, of the oxygen-oxygen pair-distribution function, g(OO)(r), which essentially describes the distribution of molecular centers. The extended Q-range and low statistical noise of these measurements has significantly reduced truncation effects and related errors in the g(OO)(r) functions obtained. From these measurements and error analysis, the position and height of the nearest neighbor maximum in g(OO)(r) were found to be 2.80(1) angstrom and 2.57(5) respectively. Numerical data for the coherent differential x-ray scattering cross-section I-X(Q), the oxygen-oxygen structure factor S-OO(Q), and the derived g(OO)(r) are provided as benchmarks for calibrating force-fields for water.

  • 117.
    Stevensson, Baltzar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Edén, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK), Avdelningen för fysikalisk kemi.
    Interpolation by fast Wigner transform for rapid calculations of magnetic resonance spectra from powders2011Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, nr 12, s. 124104-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We introduce a novel interpolation strategy, based on nonequispaced fast transforms involving spherical harmonics or Wigner functions, for efficient calculations of powder spectra in (nuclear) magnetic resonance spectroscopy. The fast Wigner transform (FWT) interpolation operates by minimizing the time-consuming calculation stages, by sampling over a small number of Gaussian spherical quadrature (GSQ) orientations that are exploited to determine the spectral frequencies and amplitudes from a 10-70 times larger GSQ set. This results in almost the same orientational averaging accuracy as if the expanded grid was utilized explicitly in an order of magnitude slower computation. FWT interpolation is applicable to spectral simulations involving any time-independent or time-dependent and noncommuting spin Hamiltonian. We further show that the merging of FWT interpolation with the well-established ASG procedure of Alderman, Solum and Grant [J. Chem. Phys. 134, 3717 (1986)] speeds up simulations by 2-7 times relative to using ASG alone (besides greatly extending its scope of application), and between 1-2 orders of magnitude compared to direct orientational averaging in the absence of interpolation. Demonstrations of efficient spectral simulations are given for several magic-angle spinning scenarios in NMR, encompassing half-integer quadrupolar spins and homonuclear dipolar-coupled (13)C systems.

  • 118. Tatarkhanov, M.
    et al.
    Fomin, E.
    Salmeron, M.
    Andersson, K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ogasawara, H.
    Pettersson, L. G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Cerda, J. I.
    The structure of mixed H2O-OH monolayer films on Ru(0001)2008Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, nr 15, s. 154109-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Scanning tunneling microscopy (STM) and x-ray absorption spectroscopy (XAS) have been used to study the structures produced by water on Ru(0001) at temperatures above 140 K. It was found that while undissociated water layers are metastable below 140 K, heating above this temperature produces drastic transformations, whereby a fraction of the water molecules partially dissociate and form mixed H2O-OH structures. X-ray photoelectron spectroscopy and XAS revealed the presence of hydroxyl groups with their O-H bond essentially parallel to the surface. STM images show that the mixed H2O-OH structures consist of long narrow stripes aligned with the three crystallographic directions perpendicular to the close-packed atomic rows of the Ru(0001) substrate. The internal structure of the stripes is a honeycomb network of H-bonded water and hydroxyl species. We found that the metastable low temperature molecular phase can also be converted to a mixed H2O-OH phase through excitation by the tunneling electrons when their energy is 0.5 eV or higher above the Fermi level. Structural models based on the STM images were used for density functional theory optimizations of the stripe geometry. The optimized geometry was then utilized to calculate STM images for comparison with the experiment.

  • 119.
    Thaning, Johan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Stevensson, Baltzar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Maliniak, Arnold
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Molecular structure extracted from residual dipolar couplings: Diphenylmethane dissolved in a nematic liquid crystal2005Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 123, nr 4, s. 044507-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes an analysis of 1H–1H residual dipolar couplings (RDCs)in diphenylmethane (DPM) dissolved in a nematic liquid crystal, reportedby Celebre et al. [J. Chem. Phys. 118, 6417 (2003)]. Inthat article, the conformational distribution function for DPM was extractedfrom the RDCs, using the additive potential (AP) model whichis based on the molecular-field theory. The AP approach isa powerful, and frequently used, tool for analysis of thenuclear-magnetic-resonance (NMR) parameters in liquid crystals. It requires, however, apriori knowledge of the functional form of the torsional potential,which may even for a simple molecule, such as DPM,be complicated to determine. Here, we analyze the same setof the RDCs using our APME procedure, which is ahybrid model based on the AP approach and maximum entropy(ME) theory. The APME procedure does not require any assumptionsabout the functional form of the torsional potential and, incontrast with the ME method, is applicable to weakly orderedsystems. In the investigation reported in the present study, theresults from the APME analysis are in good agreement withthe AP interpretation, whereas the ME approach essentially fails inthe extraction of the conformational distribution function for DPM.

  • 120. Thomson, E. S.
    et al.
    Hansen-Goos, Hendrik
    Wettlaufer, J. S.
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Wilen, L. A.
    Grain boundary melting in ice2013Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, nr 12, s. 124707-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We describe an optical scattering study of grain boundary premelting in water ice. Ubiquitous long ranged attractive polarization forces act to suppress grain boundary melting whereas repulsive forces originating in screened Coulomb interactions and classical colligative effects enhance it. The liquid enhancing effects can be manipulated by adding dopant ions to the system. For all measured grain boundaries this leads to increasing premelted film thickness with increasing electrolyte concentration. Although we understand that the interfacial surface charge densities q(s) and solute concentrations can potentially dominate the film thickness, we cannot directly measure them within a given grain boundary. Therefore, as a framework for interpreting the data we consider two appropriate q(s) dependent limits; one is dominated by the colligative effect and other is dominated by electrostatic interactions.

  • 121.
    Todde, Guido
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Hovmöller, Sven
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Laaksonen, Aatto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Stockholms universitet, Science for Life Laboratory (SciLifeLab).
    Influence of mutations at the proximal histidine position on the Fe-O-2 bond in hemoglobin from density functional theory2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, nr 9, artikkel-id 095101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Four mutated hemoglobin (Hb) variants and wild type hemoglobin as a reference have been investigated using density functional theory methods focusing on oxygen binding. Dispersion-corrected B3LYP functional is used and found to provide reliable oxygen binding energies. It also correctly reproduces the spin distribution of both bound and free heme groups as well as provides correct geometries at their close vicinity. Mutations in hemoglobin are not only an intrigued biological problem and it is also highly important to understand their effects from a clinical point of view. This study clearly shows how even small structural differences close to the heme group can have a significant effect in reducing the oxygen binding of mutated hemoglobins and consequently affecting the health condition of the patient suffering from the mutations. All of the studied mutated Hb variants did exhibit much weaker binding of molecular oxygen compared to the wild type of hemoglobin.

  • 122. Tokushima, Takashi
    et al.
    Horikawa, Yuka
    Arai, Hidemi
    Harada, Yoshihisa
    Takahashi, Osamu
    Pettersson, Lars G.M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Shin, Shik
    Polarization dependent resonant x-ray emission spectroscopy of D2O and H2O water: Assignment of the local molecular orbital symmetry2012Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, nr 4, s. 044517-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The polarization dependence of the split two peaks in the lone-pair region in the x-ray emission spectra has been determined at several different excitation energies for both D2O and H2O water. In contrast to predictions based on a narrow range of local water structures where the two peaks would be of different molecular orbital symmetry and arise from, respectively, intact and dissociated molecules, we show that the two peaks in the lone-pair region are both of lone-pair 1b(1) orbital symmetry. The results support the interpretation that the two peaks appear due to fluctuations between two distinct different main structural environments.

  • 123. Tom, Brian A.
    et al.
    Zhaunerchyk, Vitali
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Wiczer, Michael B.
    Mills, Andrew A.
    Crabtree, Kyle N.
    Kaminska, Magdalena
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Geppert, Wolf D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hamberg, Mathias
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    af Ugglas, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Vigren, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    van der Zande, Wim J.
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    McCall, Benjamin J.
    Dissociative recombination of highly enriched para-H-3(+)2009Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, nr 3, s. 31101-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The determination of the dissociative recombination rate coefficient of H-3(+) has had a turbulent history, but both experiment and theory have recently converged to a common value. Despite this convergence, it has not been clear if there should be a difference between the rate coefficients for ortho-H-3(+) and para-H-3(+). A difference has been predicted theoretically and could conceivably impact the ortho:para ratio of H-3(+) in the diffuse interstellar medium, where H-3(+) has been widely observed. We present the results of an experiment at the CRYRING ion storage ring in which we investigated the dissociative recombination of highly enriched (similar to 83.6%) para-H-3(+) using a supersonic expansion source that produced ions with T-rot similar to 60-100 K. We observed an increase in the low energy recombination rate coefficient of the enriched para-H-3(+) by a factor of similar to 1.25 in comparison to H-3(+) produced from normal H-2 (ortho:para=3:1). The ratio of the rate coefficients of pure para-H-3(+) to that of pure ortho-H-3(+) is inferred to be similar to 2 at low collision energies; the corresponding ratio of the thermal rate coefficients is similar to 1.5 at electron temperatures from 60 to 1000 K. We conclude that this difference is unlikely to have an impact on the interstellar ortho:para ratio of H-3(+).

  • 124. Usula, M.
    et al.
    Mocci, Francesca
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). University of Cagliari .
    Marincola, F. Cesare
    Porcedda, S.
    Gontrani, L.
    Caminiti, R.
    The structural organization of N-methyl-2-pyrrolidone plus water mixtures: A densitometry, x-ray diffraction, and molecular dynamics study2014Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, nr 12, s. 124503-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A combined approach of molecular dynamics simulations, wide angle X-ray scattering experiments, and density measurements was employed to study the structural properties of N-methyl-2-pyrrolidone (NMP) + water mixtures over the whole concentration range. Remarkably, a very good agreement between computed and experimental densities and diffraction patterns was achieved, especially if the effect of the mixture composition on NMP charges is taken into account. Analysis of the intermolecular organization, as revealed by the radial and spatial distribution functions of relevant solvent atoms, nicely explained the density maximum observed experimentally.

  • 125. Vehkamaki, Hanna
    et al.
    McGrath, Matthew J.
    Kurten, Theo
    Julin, Jan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Lehtinen, Kari E. J.
    Kulmala, Markku
    Rethinking the application of the first nucleation theorem to particle formation2012Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, nr 9, s. 094107-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The critical cluster is the threshold size above which a cluster will be more likely to grow than to evaporate. In field and laboratory measurements of new particle formation, the number of molecules of a given species in the critical cluster is commonly taken to be the slope of the log-log plot of the formation rate versus the concentration of the species. This analysis is based on an approximate form of the first nucleation theorem, which is derived with the assumption that there are no minima in the free energy surface prior to the maximum at the critical size. However, many atmospherically relevant systems are likely to exhibit such minima, for example, ions surrounded by condensable vapour molecules or certain combinations of acids and bases. We have solved numerically the birth-death equations for both an electrically neutral one-component model system with a local minimum at pre-critical sizes and an ion-induced case. For the ion-induced case, it is verified that the log-log slope of the nucleation rate versus particle concentration plot gives accurately the difference between the cluster sizes at the free energy maximum and minimum, as is expected from the classical form of the ion-induced nucleation rate. However, the results show that applying the nucleation theorem to neutral systems with stable pre-nucleation clusters may lead to erroneous interpretations about the nature of the critical cluster. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3689227]

  • 126. Vincent, Jonathan
    et al.
    Andersson, Magnus
    Eklund, Mattias
    Wöhri, Annemarie B
    Odelius, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Malmerberg, Erik
    Kong, Qingyu
    Wulff, Michael
    Neutze, Richard
    Davidsson, Jan
    Solvent dependent structural perturbations of chemical reaction intermediates visualized by time-resolved x-ray diffraction.2009Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, nr 15, s. 154502-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ultrafast time-resolved wide angle x-ray scattering from chemical reactions in solution has recently emerged as a powerful technique for determining the structural dynamics of transient photochemical species. Here we examine the structural evolution of photoexcited CH(2)I(2) in the nonpolar solvent cyclohexane and draw comparisons with a similar study in the polar solvent methanol. As with earlier spectroscopic studies, our data confirm a common initial reaction pathway in both solvents. After photoexcitation, CH(2)I(2) dissociates to form CH(2)I* + I*. Iodine radicals remaining within the solvent cage recombine with a nascent CH(2)I* radical to form the transient isomer CH(2)I-I, whereas those which escape the solvent cage ultimately combine to form I(2) in cyclohexane. Moreover, the transient isomer has a lifetime approximately 30 times longer in the nonpolar solvent. Of greater chemical significance is the property of time-resolved wide angle x-ray diffraction to accurately determine the structure of the of CH(2)I-I reaction intermediate. Thus we observe that the transient iodine-iodine bond is 0.07 A+/-0.04 A shorter in cyclohexane than in methanol. A longer iodine-iodine bond length for the intermediate arises in methanol due to favorable H-bond interaction with the polar solvent. These findings establish that time-resolved x-ray diffraction has sufficient sensitivity to enable solvent dependent structural perturbations of transient chemical species to be accurately resolved.

  • 127. Waluyo, Iradwikanari
    et al.
    Huang, Congcong
    Nordlund, Dennis
    Bergmann, Uwe
    Weiss, Thomas M.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    The structure of water in the hydration shell of cations from x-ray Raman and small angle x-ray scattering measurements2011Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, nr 6, s. 064513-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    X-ray Raman scattering (XRS) spectroscopy and small angle x-ray scattering (SAXS) are used to study water in aqueous solutions of NaCl, MgCl2, and AlCl3 with the particular aim to provide information about the structure of the hydration shells of the cations. XRS spectra show that Na+ weakens the hydrogen bonds of water molecules in its vicinity, similar to the effect of increased temperature and pressure. Mg2+ and Al3+, on the other hand, cause formation of short and strong hydrogen bonds between the surrounding water molecules. SAXS data show that Mg2+ and Al3+ form tightly bound hydration shells that give a large density contrast in the scattering data. From the form factor extracted from the SAXS data, we found that Mg2+ and Al3+ have, respectively, an equivalent of one and one and a half stable hydration shells that appear as a density contrast. In addition, we estimated that the density of water in the hydration shells of Mg2+ and Al3+ is, respectively, ~61% and ~71% higher than in bulk water.

  • 128. Waluyo, Iradwikanari
    et al.
    Nordlund, Dennis
    Bergmann, Uwe
    Pettersson, Lars G.M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Increased Fraction of Weakened Hydrogen Bonds of Water in AOT Reverse Micelles2009Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, s. 031103-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Water in aerosol OT reverse micelles has been extensively studied as a model system for nanoconfined water. Results from previous vibrational studies suggest that water confined this way has slower dynamics compared to bulk water; however, the effects on the hydrogen bonding network are unclear. From our study of the structure of water hydrogen bonding using x-ray Raman spectroscopy, we found an increased fraction of weakened hydrogen bonds upon confinement, similar to the effect seen in temperature increase and NaCl solvation, as evidenced by the changes in specific spectral features

  • 129. Waluyo, Iradwikanari
    et al.
    Nordlund, Dennis
    Bergmann, Uwe
    Schlesinger, Daniel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    A different view of structure-making and structure-breaking in alkali halide aqueous solutions through x-ray absorption spectroscopy2014Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, nr 24, s. 244506-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    X-ray absorption spectroscopy measured in transmission mode was used to study the effect of alkali and halide ions on the hydrogen-bonding (H-bonding) network of water. Cl- and Br- are shown to have insignificant effect on the structure of water while I-locally weakens the H-bonding, as indicated by a sharp increase of the main-edge feature in the x-ray absorption spectra. All alkali cations act as structure-breakers in water, weakening the H-bonding network. The spectral changes are similar to spectra of high density ices where the 2nd shell has collapsed due to a break-down of the tetrahedral structures, although here, around the ions, the breakdown of the local tetrahedrality is rather due to non-directional H-bonding to the larger anions. In addition, results from temperature-dependent x-ray Raman scattering measurements of NaCl solution confirm the H-bond breaking effect of Na+ and the effect on the liquid as similar to an increase in temperature.

  • 130. Wang, Han
    et al.
    Odelius, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Prendergast, David
    A combined multi-reference pump-probe simulation method with application to XUV signatures of ultrafast methyl iodide photodissociation2019Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, nr 12, artikkel-id 124106Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    UV pump-XUV/X-ray probe measurements have been successfully applied in the study of photo-induced chemical reactions. Although rich element-specific electronic structure information is accessible within XUV/X-ray (inner-shell) absorption spectra, it can be difficult to interpret the chemistry directly from the spectrum without supporting theoretical simulations. A multireference method to completely simulate UV pump-XUV/X-ray probe measurement has been developed and applied to study the methyl iodide photodissociation process. Multireference, fewest-switches surface hopping (FSSH) trajectories were used to explore the coupled electronic and ionic dynamics upon photoexcitation of methyl iodide. Interpretation of previous measurements is provided by associated multireference, restricted active space, inner-shell spectral simulations. This combination of multireference FSSH trajectories and XUV spectra provides an interpretation of transient features appearing in previous measurements within the first 100 fs after photoexcitation and validates the significant branching ratio in the final excited-state population. This methodology should prove useful for interpretation of the increasing number of inner-shell probe studies of molecular excited states or for directing new experiments toward interesting regions of the potential energy landscape.

  • 131.
    Wang, Yong-Lei
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK). Stanford University, USA.
    Li, Bin
    Sarman, Sten
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Laaksonen, Aatto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Microstructures and dynamics of tetraalkylphosphonium chloride ionic liquids2017Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, nr 22, artikkel-id 224502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Atomistic simulations have been performed to investigate the effect of aliphatic chain length in tetraalkylphosphonium cations on liquid morphologies, microscopic ionic structures, and dynamical quantities of tetraalkylphosphonium chloride ionic liquids. The liquid morphologies are characterized by sponge-like interpenetrating polar and apolar networks in ionic liquids consisting of tetraalkylphosphonium cations with short aliphatic chains. The lengthening aliphatic chains in tetraalkylphosphonium cations lead to polar domains consisting of chloride anions and central polar groups in cations being partially or totally segregated in ionic liquid matrices due to a progressive expansion of apolar domains in between. Prominent polarity alternation peaks and adjacency correlation peaks are observed at low and high q range in total X-ray scattering structural functions, respectively, and their peak positions gradually shift to lower q values with lengthening aliphatic chains in tetraalkylphosphonium cations. The charge alternation peaks registered in the intermediate q range exhibit complicated tendencies due to a cancellation of peaks and anti-peaks in partial structural functions for ionic subcomponents. The particular microstructures and liquid morphologies in tetraalkylphosphonium chloride ionic liquids intrinsically contribute to distinct dynamics characterized by mean square displacements, van Hove correlation functions, and non-Gaussian parameters for ionic species in the heterogeneous ionic environment. Most tetraalkylphosphonium cations have higher translational mobilities than their partner anions due to strong coordination of chloride anions with central polar groups in tetraalkylphosphonium cations through strong Coulombic and hydrogen bonding interactions. The increase of aliphatic chain length in tetraalkylphosphonium cations leads to a concomitant shift of van Hove correlation functions and non-Gaussian parameters to larger radial distances and longer time scales, respectively, indicating the enhanced translational dynamical heterogeneities of tetraalkylphosphonium cations and the corresponding chloride anions.

  • 132. Wang, Yong-Lei
    et al.
    Sarman, Sten
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Kloo, Lars
    Antzutkin, Oleg N.
    Glavatskih, Sergei
    Laaksonen, Aatto
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för material- och miljökemi (MMK).
    Solvation structures of water in trihexyltetradecylphosphonium-orthoborate ionic liquids2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, nr 6, artikkel-id 064507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Atomistic molecular dynamics simulations have been performed to investigate effective interactions of isolated water molecules dispersed in trihexyltetradecylphosphonium-orthoborate ionic liquids (ILs). The intrinsic free energy changes in solvating one water molecule from gas phase into bulk IL matrices were estimated as a function of temperature, and thereafter, the calculations of potential of mean force between two dispersed water molecules within different IL matrices were performed using umbrella sampling simulations. The systematic analyses of local ionic microstructures, orientational preferences, probability and spatial distributions of dispersed water molecules around neighboring ionic species indicate their preferential coordinations to central polar segments in orthoborate anions. The effective interactions between two dispersed water molecules are partially or totally screened as their separation distance increases due to interference of ionic species in between. These computational results connect microscopic anionic structures with macroscopically and experimentally observed difficulty in completely removing water from synthesized IL samples and suggest that the introduction of hydrophobic groups to central polar segments and the formation of conjugated ionic structures in orthoborate anions can effectively reduce residual water content in the corresponding IL samples.

  • 133. Wernet, Ph.
    et al.
    Leitner, T.
    Josefsson, Ida
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mazza, T.
    Miedema, P. S.
    Schröder, H.
    Beye, M.
    Kunnus, K.
    Schreck, S.
    Radcliffe, P.
    Düsterer, S.
    Meyer, M.
    Odelius, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Föhlisch, A.
    Communication: Direct evidence for sequential dissociation of gas-phase Fe(CO)(5) via a singlet pathway upon excitation at 266 nm2017Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, nr 21, artikkel-id 211103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We prove the hitherto hypothesized sequential dissociation of Fe(CO)(5) in the gas phase upon photoexcitation at 266 nm via a singlet pathway with time-resolved valence and core-level photoelectron spectroscopy with an x-ray free-electron laser. Valence photoelectron spectra are used to identify free CO molecules and to determine the time constants of stepwise dissociation to Fe(CO)(4) within the temporal resolution of the experiment and further to Fe(CO)(3) within 3 ps. Fe 3p core-level photoelectron spectra directly reflect the singlet spin state of the Fe center in Fe(CO)(5), Fe(CO)(4), and Fe(CO)(3) showing that the dissociation exclusively occurs along a singlet pathway without triplet-state contribution. Our results are important for assessing intra- and intermolecular relaxation processes in the photodissociation dynamics of the prototypical Fe(CO)(5) complex in the gas phase and in solution, and they establish time-resolved core-level photoelectron spectroscopy as a powerful tool for determining the multiplicity of transition metals in photochemical reactions of coordination complexes.

  • 134.
    Wikfeldt, Kjartan Thor
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Huang, Congcong
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Enhanced small-angle scattering connected to the Widom line in simulations of supercooled waterInngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present extensive simulation results on the TIP4P/2005 water model and show that it displays significantly enhanced small-angle scattering in the supercooled regime. The simulations exhibit a Widom line (TW), emanating from a liquid-liquid critical point (LLCP) in the supercooled region; TW is characterized by a maximal Ornstein-Zernike correlation length and strong small-angle scattering. The good agreement between the simulated small-angle scattering and recent experimental SAXS data [Huang et al., J. Chem. Phys. 133, 134504 (2010)] thus provides indirect evidence for the existence of a Widom line in supercooled water; both the LLCP and singularity-free (SF) scenarios are however consistent with the presence of TW. Simulations performed at 1, 1,000 and 1,500 bar show an increasing abruptness of a high-density (HDL) to low-density (LDL) liquid crossover associated with crossing TW, while simulations at 2,000 bar show a very gradual transition at lower temperatures indicating that the critical pressure (whether at T=0, as in the SF scenario, or above as in the LLCP scenario) is below 2,000 bar in this simulation model. Maxima in the isothermal compressibility and negative thermal expansion coefficient nearly coincide with TW at 1, 1,000 and 1,500 bar. Analysis of the tetrahedrality parameter Q reveals that the HDL-LDL structural transition is very sharp at 1,000 and 1,500 bar, and that structural fluctuations become strongly coupled to density fluctuations upon approaching TW. Furthermore, the tetrahedrality distribution becomes bimodal at ambient temperatures, an observation that possibly provides a link between the HDL-LDL transition and the structural bimodality in liquid water indicated by x-ray spectroscopic techniques.

  • 135.
    Wikfeldt, Kjartan Thor
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Leetmaa, Mikael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mace, Amber
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Oxygen-oxygen correlations in liquid water: Addressing the discrepancy between diffraction and EXAFS using a novel multiple –data set fitting technique2010Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, nr 10, artikkel-id 104513Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first peak of the oxygen-oxygen pair-correlation function (O-O PCF) is a critical measure of the first coordination shell distances in liquid water. Recently, a discrepancy has been uncovered between diffraction and extended x-ray absorption fine-structure (EXAFS) regarding the height and position of this peak, where EXAFS gives a considerably more well-defined peak at a shorter distance compared with diffraction results. This discrepancy is here investigated through a new multiple data set structure modeling technique, SpecSwap-RMC, based on the reverse Monte Carlo (RMC) method. Fitting simultaneously to both EXAFS and a diffraction-based O-O PCF shows that, even though the reported EXAFS results disagree with diffraction, the two techniques can be reconciled by taking into account a strong contribution from the focusing effect originating from nearly linear hydrogen bonds. This many-body contribution, which is usually neglected in RMC modeling of EXAFS data, is included in the fits by precomputing and storing EXAFS signals from real-space multiple-scattering calculations on a large number of unique water clusters. On the other hand, fitting also the O-O PCF from diffraction is seen to enhance the amount of structural disorder in the joint fit. Thus, both nearly linear hydrogen bonds and local structural disorder are important to reproduce diffraction and EXAFS simultaneously. This work also illustrates a few of many possible uses of the SpecSwap-RMC method in modeling disordered materials, particularly for fitting computationally demanding techniques and combining multiple data sets.

  • 136.
    Wikfeldt, Thor Kjartan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Huang, C.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Enhanced small-angle scattering connected to the Widom line in simulations of supercooled water2011Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, nr 21, s. 214506-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present extensive simulations on the TIP4P/2005 water model showing significantly enhanced small-angle scattering (SAS) in the supercooled regime. The SAS is related to the presence of a Widom line (TW) characterized by maxima in thermodynamic response functions and Ornstein-Zernike correlation length. Recent experimental small-angle x-ray scattering data [Huang et al., J. Chem. Phys. 133, 134504 (2010)] are excellently reproduced, albeit with an increasing temperature offset at lower temperatures. Assuming the same origin of the SAS in experiment and model this suggests the existence of a Widom line also in real supercooled water. Simulations performed at 1000 bar show an increased abruptness of a crossover from dominating high-density (HDL) to dominating low-density (LDL) liquid and strongly enhanced SAS associated with crossing TW, consistent with a recent determination of the critical pressure of TIP4P/2005 at 1350 bar. Furthermore, good agreement with experimental isothermal compressibilities at 1000, 1500, and 2000 bar shows that the high pressure supercooled thermodynamic behavior of water is well described by TIP4P/2005. Analysis of the tetrahedrality parameter Q reveals that the HDL-LDL structural transition is very sharp at 1000 bar, and that structural fluctuations become strongly coupled to density fluctuations upon approaching TW. Furthermore, the tetrahedrality distribution becomes bimodal at ambient temperatures, an observation that possibly provides a link between HDL-LDL fluctuations and the structural bimodality in liquid water indicated by x-ray spectroscopic techniques. Computed x-ray absorption spectra are indeed found to show sensitivity to the tetrahedrality parameter.

  • 137. Wu, Guorong
    et al.
    Neville, Simon P.
    Schalk, Oliver
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. National Research Council, Canada.
    Sekikawa, Taro
    Ashfold, Michael N. R.
    Worth, Graham A.
    Stolow, Albert
    Excited state non-adiabatic dynamics of N-methylpyrrole: A time-resolved photoelectron spectroscopy and quantum dynamics study2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, nr 1, artikkel-id 014309Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamics of N-methylpyrrole following excitation at wavelengths in the range 241.5-217.0 nm were studied using a combination of time-resolved photoelectron spectroscopy (TRPES), ab initio quantum dynamics calculations using the multi-layer multi-configurational time-dependent Hartree method, as well as high-level photoionization cross section calculations. Excitation at 241.5 and 236.2 nm results in population of the A(2)(pi sigma*) state, in agreement with previous studies. Excitation at 217.0 nm prepares the previously neglected B-1(pi 3p(y)) Rydberg state, followed by prompt internal conversion to the A(2)(pi sigma*) state. In contrast with the photoinduced dynamics of pyrrole, the lifetime of the wavepacket in the A(2)(pi sigma*) state was found to vary with excitation wavelength, decreasing by one order of magnitude upon tuning from 241.5 nm to 236.2 nm and by more than three orders of magnitude when excited at 217.0 nm. The order of magnitude difference in lifetimes measured at the longer excitation wavelengths is attributed to vibrational excitation in the A(2)(pi sigma*) state, facilitating wavepacket motion around the potential barrier in the N-CH3 dissociation coordinate.

  • 138. Wu, Guorong
    et al.
    Neville, Simon P.
    Schalk, Oliver
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. National Research Council Canada, Canada.
    Sekikawa, Taro
    Ashfold, Michael N. R.
    Worth, Graham A.
    Stolow, Albert
    Excited state non-adiabatic dynamics of pyrrole: A time-resolved photoelectron spectroscopy and quantum dynamics study2015Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 142, nr 7, artikkel-id 74302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamics of pyrrole excited at wavelengths in the range 242-217 nm are studied using a combination of time-resolved photoelectron spectroscopy and wavepacket propagations performed using the multi-configurational time-dependent Hartree method. Excitation close to the origin of pyrrole's electronic spectrum, at 242 and 236 nm, is found to result in an ultrafast decay of the system from the ionization window on a single timescale of less than 20 fs. This behaviour is explained fully by assuming the system to be excited to the A(2)(pi sigma*) state, in accord with previous experimental and theoretical studies. Excitation at shorter wavelengths has previously been assumed to result predominantly in population of the bright A(1)(pi pi*) and B-2(pi pi*) states. We here present time-resolved photoelectron spectra at a pump wavelength of 217 nm alongside detailed quantum dynamics calculations that, together with a recent reinterpretation of pyrrole's electronic spectrum [S. P. Neville and G. A. Worth, J. Chem. Phys. 140, 034317 (2014)], suggest that population of the B-1(pi sigma*) state (hitherto assumed to be optically dark) may occur directly when pyrrole is excited at energies in the near UV part of its electronic spectrum. The B-1(pi sigma*) state is found to decay on a timescale of less than 20 fs by both N-H dissociation and internal conversion to the A(2)(pi sigma*) state.

  • 139. Yamazoe, Kosuke
    et al.
    Miyawaki, Jun
    Niwa, Hideharu
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Harada, Yoshihisa
    Measurements of ultrafast dissociation in resonant inelastic x-ray scattering of water2019Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, nr 20, artikkel-id 204201Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There has been a discussion on the interpretation of the resonant inelastic x-ray scattering (RIXS) spectra of liquid water in terms of either different structural environments or that core hole dynamics can generate well-resolved dissociative spectral components. We have used RIXS with high resolution in the OH stretch vibration energy part, at extremely high overtones going toward the continuum of full OH bond breakage, to identify the amount of dissociative contributions in the valence band RIXS spectra at different excitation energies. We observe that at low excitation energies, corresponding to population of states with strongly antibonding character, the valence band RIXS spectra have a large contribution from a well-resolved dissociative feature. Instead, at higher excitations, this spectral component diminishes and becomes a weak structure on the high-energy side of one of the spectral peaks related to the 1b(1), state from tetrahedral configurations. This result brings both interpretations to be essential for the understanding of RIXS spectra of liquid water.

  • 140. Zagorodskikh, Sergey
    et al.
    Eland, John H. D.
    Zhaunerchyk, Vitali
    Mucke, Melanie
    Squibb, Richard J.
    Linusson, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Feifel, Raimund
    Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal)2016Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, nr 12, artikkel-id 124302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Site-specific fragmentation upon 1s photoionisation of acetaldehyde has been studied using synchrotron radiation and a multi-electron-ion coincidence technique based on a magnetic bottle. Experimental evidence is presented that bond rupture occurs with highest probability in the vicinity of the initial charge localisation and possible mechanisms are discussed. We find that a significant contribution to site-specific photochemistry is made by different fragmentation patterns of individual quantum states populated at identical ionisation energies.

  • 141. Zerbetto, Mirco
    et al.
    Polimeno, Antonino
    Kotsyubynskyy, Dmytro
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Ghalebani, Leila
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi.
    Kowalewski, Jozef
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för fysikalisk kemi, oorganisk kemi och strukturkemi, Avdelningen för fysikalisk kemi.
    Meirovitch, Eva
    Olsson, Ulrika
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    An integrated approach to NMR spin relaxation in flexible biomolecules: Application to β-D-glucopyranosyl-(1→6)-α-D-mannopyranosyl-OMe2009Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, nr 23, s. p234501-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The description of the reorientational dynamics of flexible molecules is a challenging task, in particular when the rates of internal and global motions are comparable. The commonly used simple mode-decoupling models are based on the assumption of statistical independence between these motions. This assumption is not valid when the time scale separation between their rates is small, a situation that was found to arise in oligosaccharides in the context of certain internal motions. To make possible the interpretation of NMR spin relaxation data from such molecules, we developed a comprehensive approach generally applicable to flexible rotators with one internal degree of freedom. This approach integrates a stochastic description of coupled global tumbling and internal torsional motion, quantum chemical calculations of the local potential and the local geometry at the site of the restricted torsion, and hydrodynamics-based calculations of the diffusive properties. The method is applied to the disaccharide -D-Glcp-(16)--D-[6-13C]-Manp-OMe dissolved in a DMSO-d6/D2O cryosolvent. The experimental NMR relaxation parameters, associated with the 13CH2 probe residing at the glycosidic linkage, include 13C T1 and T2 and 13C-{1H} nuclear Overhauser enhancement (NOE) as well as longitudinal and transverse dipole-dipole cross-correlated relaxation rates, acquired in the temperature range of 253–293 K. These data are predicted successfully by the new theory with only the H–C–H angle allowed to vary. Previous attempts to fit these data using mode-decoupling models failed.

  • 142. Zerbetto, Mirco
    et al.
    Polimeno, Antonino
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Widmalm, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för organisk kemi.
    Glycosidic linkage flexibility: The psi torsion angle has a bimodal distribution in alpha-L-Rhap-(1 -> 2)-alpha-L-Rhap-OMe as deduced from C-13 NMR spin relaxation2020Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 152, nr 3, artikkel-id 035103Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The molecular dynamics (MD) computer simulation technique is powerful for the investigation of conformational equilibrium properties of biomolecules. In particular, free energy surfaces of the torsion angles (those degrees of freedom from which the geometry mostly depends) allow one to access conformational states, as well as kinetic information, i.e., if the transitions between conformational states occur by simple jumps between wells or if conformational regions close to these states also are populated. The information obtained from MD simulations may depend substantially on the force field employed, and thus, a validation procedure is essential. NMR relaxation data are expected to be highly sensitive to the details of the torsional free energy surface. As a case-study, we consider the disaccharide alpha-l-Rhap-(1 -> 2)-alpha-l-Rhap-OMe that features only two important torsion angles, phi and psi, which define the interglycosidic orientation of the sugar residues relative to each other, governed mainly by the exo-anomeric effect and steric interactions, respectively. In water, a psi(-) state is preferred, whereas in DMSO, it is a psi(+) state, suggesting inherent flexibility at the torsion angle. MD simulations indicated that bistable potentials describe the conformational region well. To test whether a unimodal distribution suffices or if a bimodal distribution better represents molecular conformational preferences, we performed an alchemical morphing of the torsional free energy surface and computed T-1, T-2, and NOE C-13 NMR relaxation data that were compared to experimental data. All three NMR observables are substantially affected by the morphing procedure, and the results strongly support a bimodal Boltzmann equilibrium density with a major and a minor conformational state bisected at psi approximate to 0 degrees, in accord with MD simulations in an explicit solvent.

  • 143.
    Zettergren, Henning
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Johansson, H. A. B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Schmidt, Henning T.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Jensen, J.
    Hvelplund, P.
    Tomita, S.
    Wang, Y.
    Martin, F.
    Alcami, M.
    Manil, B.
    Maunoury, L.
    Huber, B. A.
    Cederquist, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Magic and hot giant fullerenes formed inside ion irradiated weakly bound C-60 clusters2010Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, nr 10, s. 104301-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We find that the most stable fullerene isomers, C-70-C-94, form efficiently in close-to central collisions between keV atomic ions and weakly bound clusters of more than 15 C-60-molecules. We observe extraordinarily high yields of C-70 and marked preferences for C-78 and C-84. Larger even-size carbon molecules, C-96-C-180, follow a smooth log-normal (statistical) intensity distribution. Measurements of kinetic energies indicate that C-70-C-94 mainly are formed by coalescence reactions between small carbon molecules and Coo, while C-n with n >= 96 are due to self-assembly (of small molecules) and shrinking hot giant fullerenes.

  • 144.
    Zhaunerchyk, Vitali
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Geppert, Wolf D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Rosen, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Vigren, Erik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hamberg, Mathias
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Kaminska, Magdalena
    Kashperka, Iryna
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    af Ugglas, Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Semaniak, Jacek
    Larsson, Mats
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Thomas, Richard D.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Investigation into the vibrational yield of OH products in the OH plus H plus H channel arising from the dissociative recombination of H3O+2009Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, nr 21, s. 214302-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The vibrational population of the hydroxyl radical, OH, formed in the OH+H+H channel arising from the dissociative recombination of the hydronium ion, H3O+, has been investigated at the storage ring CRYRING using a position-sensitive imaging detector. Analysis shows that the OH fragments are predominantly produced in the v=0 and v=1 states with almost equal probabilities. This observation is in disagreement with earlier FALP experiments, which reported OH(v=0) as the dominant product. Possible explanations for this difference are discussed.

  • 145.
    Zhovtobriukh, Iurii
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Besley, Nicholas A.
    Fransson, Thomas
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Relationship between x-ray emission and absorption spectroscopy and the local H-bond environment in water2018Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, nr 14, artikkel-id 144507Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The connection between specific features in the water X-ray absorption spectrum and X-ray emission spectrum (XES) and the local H-bond coordination is studied based on structures obtained from path-integral molecular dynamics simulations using either the opt-PBE-vdW density functional or the MB-pol force field. Computing the XES spectrum using all molecules in a snapshot results in only one peak in the lone-pair (1b(1)) region, while the experiment shows two peaks separated by 0.8-0.9 eV. Different H-bond configurations were classified based on the local structure index (LSI) and a geometrical H-bond cone criterion. We find that tetrahedrally coordinated molecules characterized by high LSI values and two strong donated and two strong accepted H-bonds contribute to the lowenergy 1b(1) emission peak and to the post-edge region in absorption. Molecules with the asymmetric H-bond environment with one strong accepted H-bond and one strong donated H-bond and low LSI values give rise to the high energy 1b(1) peak in the emission spectrum and mainly contribute to the pre-edge and main-edge in the absorption spectrum. The 1b(1) peak splitting can be increased to 0.62 eV by imposing constraints on the H-bond length, i.e., for very tetrahedral structures short H-bonds (less than 2.68 angstrom) and for very asymmetric structures elongated H-bonds (longer than 2.8 angstrom). Such structures are present, but under-represented, in the simulations which give more of an average of the two extremes.

  • 146.
    Zhovtobriukh, Iurii
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Norman, Patrick
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    X-ray absorption spectrum simulations of hexagonal ice2019Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, nr 3, artikkel-id 034501Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We calibrate basis sets and performance of two theoretical approaches to compute X-ray absorption spectra (XAS) of condensed water by comparison to experiments on hexagonal ice Ih. We apply both the transition-potential half-core-hole approach and the complex polarization propagator using four different models of the crystal with increasing oxygen and proton disorder but find poor agreement with experiments. We note that there are large variations in experimental spectra depending on detection mode and how the ice samples were prepared, which leads us to critically investigate what structures were actually prepared and measured in each case. This is done by using a Monte Carlo-based fitting technique which fits the spectra based on a library of precomputed spectra and assigns weights to contributions from different model structures. These are then used to generate O-O and O-H radial distribution functions and tetrahedrality parameters associated with each of the measured spectra. We find that all spectra are associated with sharp peaks at the oxygen positions in the perfect lattice, but with significant disorder around these positions. We suggest that presently available XAS of hexagonal ice are not fully representative of the perfect crystalline lattice, but contain varying amounts of defects and possible contributions from low-density amorphous ice.

  • 147.
    Öberg, Henrik
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Gladh, Jörgen
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Marks, Kess
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Ogasawara, H.
    Nilsson, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. SLAC National Accelerator Laboratory, USA.
    Pettersson, Lars G. M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Östrom, Henrik
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Indication of non-thermal contribution to visible femtosecond laser-induced CO oxidation on Ru(0001)2015Inngår i: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 143, nr 7, artikkel-id 074701Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We studied CO oxidation on Ru(0001) induced by 400 nm and 800 nm femtosecond laser pulses where we find a branching ratio between CO oxidation and desorption of 1: 9 and 1: 31, respectively, showing higher selectivity towards CO oxidation for the shorter wavelength excitation. Activation energies computed with density functional theory show discrepancies with values extracted from the experiments, indicating both a mixture between different adsorbed phases and importance of non-adiabatic effects on the effective barrier for oxidation. We simulated the reactions using kinetic modeling based on the two-temperature model of laser-induced energy transfer in the substrate combined with a friction model for the coupling to adsorbate vibrations. This model gives an overall good agreement with experiment except for the substantial difference in yield ratio between CO oxidation and desorption at 400 nm and 800 nm. However, including also the initial, non-thermal effect of electrons transiently excited into antibonding states of the O-Ru bond yielded good agreement with all experimental results.

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