| 1. |
- Aad, G., et al.
(författare)
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- 2015
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Ingår i: Journal of High Energy Physics. - : Springer-Verlag New York. - 1029-8479 .- 1126-6708. ; :9
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Nimmrich, Amke, 1995, et al.
(författare)
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Solvent-Dependent Structural Dynamics in the Ultrafast Photodissociation Reaction of Triiodide Observed with Time-Resolved X-ray Solution Scattering
- 2023
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 145:29, s. 15754-15765
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Tidskriftsartikel (refereegranskat)abstract
- Resolving the structural dynamics of bond breaking, bond formation, and solvation is required for a deeper understanding of solutionphase chemical reactions. In this work, we investigate the photodissociation of triiodide in four solvents using femtosecond time-resolved X-ray solution scattering following 400 nm photoexcitation. Structural analysis of the scattering data resolves the solvent-dependent structural evolution during the bond cleavage, internal rearrangements, solvent-cage escape, and bond reformation in real time. The nature and structure of the reaction intermediates during the recombination are determined, elucidating the full mechanism of photodissociation and recombination on ultrafast time scales. We resolve the structure of the precursor state for recombination as a geminate pair. Further, we determine the size of the solvent cages from the refined structures of the radical pair. The observed structural dynamics present a comprehensive picture of the solvent influence on structure and dynamics of dissociation reactions.
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| 3. |
- Caleman, Carl, et al.
(författare)
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Atomistic simulation of ion solvation in water explains surface preference of halides
- 2011
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:17, s. 6838-6842
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Tidskriftsartikel (refereegranskat)abstract
- Water is a demanding partner. It strongly attracts ions, yet some halide anions-chloride, bromide, and iodide-are expelled to the air/water interface. This has important implications for chemistry in the atmosphere, including the ozone cycle. We present a quantitative analysis of the energetics of ion solvation based on molecular simulations of all stable alkali and halide ions in water droplets. The potentials of mean force for Cl-, Br-, and I-have shallow minima near the surface. We demonstrate that these minima derive from more favorable water-water interaction energy when the ions are partially desolvated. Alkali cations are on the inside because of the favorable ion-water energy, whereas F-is driven inside by entropy. Models attempting to explain the surface preference based on one or more ion properties such as polarizability or size are shown to lead to qualitative and quantitative errors, prompting a paradigm shift in chemistry away from such simplifications.
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| 4. |
- Caleman, Carl, et al.
(författare)
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Force Field Benchmark of Organic Liquids : Density, Enthalpy of Vaporization, Heat Capacities, Surface Tension, Isothermal Compressibility, Volumetric Expansion Coefficient, and Dielectric Constant
- 2012
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Ingår i: Journal of Chemical Theory and Computation. - : American Chemical Society (ACS). - 1549-9618 .- 1549-9626. ; 8:1, s. 61-74
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Tidskriftsartikel (refereegranskat)abstract
- The chemical composition of small organic molecules is often very similar to amino acid side chains or the bases in nucleic acids, and hence there is no a priori reason why a molecular mechanics force field could not describe both organic liquids and biomolecules with a single parameter set. Here, we devise a benchmark for force fields in order to test the ability of existing force fields to reproduce some key properties of organic liquids, namely, the density, enthalpy of vaporization, the surface tension, the heat capacity at constant volume and pressure, the isothermal compressibility, the volumetric expansion coefficient, and the static dielectric constant. Well over 1200 experimental measurements were used for comparison to the simulations of 146 organic liquids. Novel polynomial interpolations of the dielectric constant (32 molecules), heat capacity at constant pressure (three molecules), and the isothermal compressibility (53 molecules) as a function of the temperature have been made, based on experimental data, in order to be able to compare simulation results to them. To compute the heat capacities, we applied the two phase thermodynamics method (Lin et al. J. Chem. Phys. 2003, 119, 11792), which allows one to compute thermodynamic properties on the basis of the density of states as derived from the velocity autocorrelation function. The method is implemented in a new utility within the GROMACS molecular simulation package, named g_dos, and a detailed expose of the underlying equations is presented. The purpose of this work is to establish the state of the art of two popular force fields, OPLS/AA (all-atom optimized potential for liquid simulation) and GAFF (generalized Amber force field), to find common bottlenecks, i.e., particularly difficult molecules, and to serve as a reference point for future force field development. To make for a fair playing field, all molecules were evaluated with the same parameter settings, such as thermostats and barostats, treatment of electrostatic interactions, and system size (1000 molecules). The densities and enthalpy of vaporization from an independent data set based on simulations using the CHARMM General Force Field (CGenFF) presented by Vanommeslaeghe et al. (J. Comput. Chem. 2010, 31, 671) are included for comparison. We find that, overall, the OPLS/AA force field performs somewhat better than GAFF, but there are significant issues with reproduction of the surface tension and dielectric constants for both force fields.
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| 5. |
- Hub, Jochen S., et al.
(författare)
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Thermodynamics of hydronium and hydroxide surface solvation
- 2014
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Ingår i: Chemical Science. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 5:5, s. 1745-1749
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Tidskriftsartikel (refereegranskat)abstract
- The concentration of hydronium and hydroxide at the water-air interface has been debated for a long time. Recent evidence from a range of experiments and theoretical calculations strongly suggests the water surface to be somewhat acidic. Using novel polarizable models we have performed potential of mean force calculations of a hydronium ion, a hydroxide ion and a water molecule in a water droplet and a water slab and we were able to rationalize that hydronium, but not hydroxide, is slightly enriched at the surface for two reasons. First, because the hydrogen bond acceptance capacity of hydronium is weaker than water and it is more favorable to have the hydronium oxygen on the surface. Second, hydroxide ions are expelled from the surface of the droplets, due to the entropy being lower when a hydroxide ion is hydrated on the surface. As a result, the water dissociation constant pK(w) increases slightly near the surface. The results are corroborated by calculations of surface tension of NaOH solutions that are in reasonable agreement with the experiment. The structural and thermodynamic interpretation of hydronium and hydroxide hydration provided by these calculations opens the route to a better understanding of atmospheric and surface chemistry.
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| 6. |
- Panman, Matthijs R, 1983, et al.
(författare)
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Observing the Structural Evolution in the Photodissociation of Diiodomethane with Femtosecond Solution X-Ray Scattering
- 2020
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 125:22
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Tidskriftsartikel (refereegranskat)abstract
- Resolving the structural dynamics of the initial steps of chemical reactions is challenging. We report the femtosecond time-resolved wide-angle x-ray scattering of the photodissociation of diiodomethane in cyclohexane. The data reveal with structural detail how the molecule dissociates into radicals, how the radicals collide with the solvent, and how they form the photoisomer. We extract how translational and rotational kinetic energy is dispersed into the solvent. We also find that 85% of the primary radical pairs are confined to their original solvent cage and discuss how this influences the downstream recombination reactions.
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| 7. |
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