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1.
  • Abel, Martin, et al. (författare)
  • Collision-induced absorption at wavelengths near 5 micrometers by dense hydrogen gas
  • 2009
  • Ingår i: J. Chem. Phys.. - : AIP Publishing. ; 131
  • Tidskriftsartikel (refereegranskat)abstract
    • Based on a recent ab initio interaction-induced dipole surface of collisionally interacting molecular hydrogen pairs H2–H2, we compute the binary absorption coefficients at wavelengths near 5 micrometers at temperatures of 77.5 and 297 K for comparison with existing laboratory measurements. We observe satisfactory agreement of the measurements with our calculations, thereby concluding an earlier study [Gustafsson et al., J. Chem. Phys. 119, 12264 (2003)], which was based on an ab initio interaction-induced dipole surface that was inadequate for the 5 micrometer band.
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2.
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3.
  • Afzelius, Mikael, et al. (författare)
  • Semiclassical calculations of collision line broadening in Raman spectra of N-2 and CO mixtures
  • 2004
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:18, s. 8616-8623
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a detailed theoretical study of pressure-broadened Raman line shapes in binary mixtures of nitrogen and carbon monoxide. The semiclassical Robert-Bonamy theory was used to calculate self-broadened Q-branch linewidths of N-2 and CO, and Lennard-Jones (LJ) potential energy surface parameters were fixed by comparing our results with extensive experimental linewidth data. For the case of N-2, the ab initio PES8 potential energy surface was investigated, however, the anisotropic repulsive part had to be reduced to ensure a good agreement with experimental linewidths. The agreement between calculations and experiments was remarkably good, both for self-broadened N-2 and CO Q-branch linewidths. Yet, our calculations were not able to predict the experimentally observed difference between Q- and S-branch linewidths of self-broadened N-2. The central results of this work are the Q-branch linewidths of N-2-CO and CO-N-2, which have been calculated through an extrapolation of the parameters of the potential energy surfaces used for self-broadened linewidths by common combination rules. (C) 2004 American Institute of Physics.
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4.
  • Agosta, Lorenzo, et al. (författare)
  • Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics
  • 2017
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 147:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Ab initio molecular dynamics simulations are reported forwater-embedded TiO2 surfaces to determine the diffusive and reactive behavior at full hydration. A three-domain model is developed for six surfaces [rutile (110), (100), and (001), and anatase (101), (100), and (001)] which describes waters as hard (irreversibly bound to the surface), soft (with reduced mobility but orientation freedom near the surface), or bulk. The model explains previous experimental data and provides a detailed picture of water diffusion near TiO2 surfaces. Water reactivity is analyzed with a graph-theoretic approach that reveals a number of reaction pathways on TiO2 which occur at full hydration, in addition to direct water splitting. Hydronium (H3O+) is identified to be a key intermediate state, which facilitates water dissociation by proton hopping between intact and dissociated waters near the surfaces. These discoveries significantly improve the understanding of nanoscale water dynamics and reactivity at TiO2 interfaces under ambient conditions.
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5.
  • Agosta, Lorenzo, et al. (författare)
  • Self-assembly of a triply periodic continuous mesophase with Fddd symmetry in simple one-component liquids
  • 2020
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:19
  • Tidskriftsartikel (refereegranskat)abstract
    • Triply periodic continuous morphologies (networks) arising as a result of the microphase separation in block copolymer melts have so far never been observed self-assembled in systems of particles with spherically symmetric interaction. We report a molecular dynamics simulation where two simple one-component liquids form upon cooling an equilibrium network with the Fddd space group symmetry. This complexity reduction in the liquid network formation in terms of the particle geometry and the number of components evidences the generic nature of this class of phase transition, suggesting opportunities for producing these structures in a variety of new systems.
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6.
  • Agosta, Lorenzo, et al. (författare)
  • Supercooled liquid-like dynamics in water near a fully hydrated titania surface : Decoupling of rotational and translational diffusion
  • 2021
  • Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 154:9
  • Tidskriftsartikel (refereegranskat)abstract
    • We report an ab initio molecular dynamics (MD) simulation investigating the effect of a fully hydrated surface of TiO2 on the water dynamics. It is found that the universal relation between the rotational and translational diffusion characteristics of bulk water is broken in the water layers near the surface with the rotational diffusion demonstrating progressive retardation relative to the translational diffusion when approaching the surface. This kind of rotation-translation decoupling has so far only been observed in the supercooled liquids approaching glass transition, and its observation in water at a normal liquid temperature is of conceptual interest. This finding is also of interest for the application-significant studies of the water interaction with fully hydrated nanoparticles. We note that this is the first observation of rotation-translation decoupling in an ab initio MD simulation of water.
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7.
  • Ahlstrand, Emma, et al. (författare)
  • Computer simulations of alkali-acetate solutions : Accuracy of the forcefields in difference concentrations
  • 2017
  • Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 147, s. 1-10
  • Tidskriftsartikel (refereegranskat)abstract
    • When proteins are solvated in electrolyte solutions that contain alkali ions, the ions interact mostlywith carboxylates on the protein surface. Correctly accounting for alkali-carboxylate interactionsis thus important for realistic simulations of proteins. Acetates are the simplest carboxylates thatare amphipathic, and experimental data for alkali acetate solutions are available and can be comparedwith observables obtained from simulations. We carried out molecular dynamics simulations of alkali acetate solutions using polarizable and non-polarizable forcefields and examined the ionacetateinteractions. In particular, activity coefficients and association constants were studied in a range of concentrations (0.03, 0.1, and 1M). In addition, quantum-mechanics (QM) based energy decomposition analysis was performed in order to estimate the contribution of polarization, electrostatics, dispersion, and QM (non-classical) effects on the cation-acetate and cation-water interactions. Simulations of Li-acetate solutions in general overestimated the binding of Li+ and acetates. In lower concentrations, the activity coefficients of alkali-acetate solutions were too high, which is suggested to be due to the simulation protocol and not the forcefields. Energy decomposition analysis suggested that improvement of the forcefield parameters to enable accurate simulations of Li-acetate solution scan be achieved but may require the use of a polarizable forcefield. Importantly, simulations with some ion parameters could not reproduce the correct ion-oxygen distances, which calls for caution in thechoice of ion parameters when protein simulations are performed in electrolyte solutions.
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8.
  • Ahmadi, Sareh, et al. (författare)
  • Molecular layers of ZnPc and FePc on Au(111) surface : Charge transfer and chemical interaction
  • 2012
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 137:8, s. 084705-
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied zinc phthalocyanine (ZnPc) and iron phthalocyanine (FePc) thick films and monolayers on Au(111) using photoelectron spectroscopy and x-ray absorption spectroscopy. Both molecules are adsorbed flat on the surface at monolayer. ZnPc keeps this orientation in all investigated coverages, whereas FePc molecules stand up in the thick film. The stronger inter-molecular interaction of FePc molecules leads to change of orientation, as well as higher conductivity in FePc layer in comparison with ZnPc, which is reflected in thickness-dependent differences in core-level shifts. Work function changes indicate that both molecules donate charge to Au; through the pi-system. However, the Fe3d derived lowest unoccupied molecular orbital receives charge from the substrate when forming an interface state at the Fermi level. Thus, the central atom plays an important role in mediating the charge, but the charge transfer as a whole is a balance between the two different charge transfer channels; pi-system and the central atom.
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9.
  • Ahmadi, Sareh, et al. (författare)
  • Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine
  • 2014
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:17, s. 174702-
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of ZnPc, from sub-monolayers to thick films, on bare and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and scanning tunneling microscopy. Our results suggest that at low coverage ZnPc lies almost parallel to the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt attraction, leading to an inhomogeneous charge distribution within the molecule and an inhomogeneous charge transfer to the molecule. ZnPc does not form a complete monolayer on the Pt surface, due to a surface-mediated intermolecular repulsion. At higher coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate interaction. Our photoemission results illustrate that ZnPc is practically decoupled from Pt, already from the second layer. Pre-deposition of iodine on Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in contact with Pt(111)-I(root 3x root 3) or Pt(111)-I(root 7x root 7), and a more homogeneous charge distribution and charge transfer at the interface. On increased ZnPc thickness iodine is dissolved in the organic film where it acts as an electron acceptor dopant.
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10.
  • Ahmadzadeh, Karan, et al. (författare)
  • Efficient implementation of isotropic cubic response functions for two-photon absorption cross sections within the self-consistent field approximation
  • 2021
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 154:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Within the self-consistent field approximation, computationally tractable expressions for the isotropic second-order hyperpolarizability have been derived and implemented for the calculation of two-photon absorption cross sections. The novel tensor average formulation presented in this work allows for the evaluation of isotropic damped cubic response functions using only similar to 3.3% (one-photon off-resonance regions) and similar to 10% (one-photon resonance regions) of the number of auxiliary Fock matrices required when explicitly calculating all the needed individual tensor components. Numerical examples of the two-photon absorption cross section in the one-photon off-resonance and resonance regions are provided for alanine-tryptophan and 2,5-dibromo-1,4-bis(2-(4-diphenylaminophenyl)vinyl)-benzene. Furthermore, a benchmark set of 22 additional small- and medium-sized organic molecules is considered. In all these calculations, a quantitative assessment is made of the reduced and approximate forms of the cubic response function in the one-photon off-resonance regions and results demonstrate a relative error of less than similar to 5% when using the reduced expression as compared to the full form of the isotropic cubic response function.
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11.
  • Ai, Yue-Jie, et al. (författare)
  • Ultrafast deactivation processes in the 2-aminopyridine dimer and the adenine-thymine base pair : Similarities and differences
  • 2010
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:6, s. 064302-
  • Tidskriftsartikel (refereegranskat)abstract
    • 2-aminopyridine dimer has frequently been used as a model system for studying photochemistry of DNA base pairs. We examine here the relevance of 2-aminopyridine dimer for a Watson-Crick adenine-thymine base pair by studying UV-light induced photodynamics along two main hydrogen bridges after the excitation to the localized (1)pi pi(*) excited-state. The respective two-dimensional potential-energy surfaces have been determined by time-dependent density functional theory with Coulomb-attenuated hybrid exchange-correlation functional (CAM-B3LYP). Different mechanistic aspects of the deactivation pathway have been analyzed and compared in detail for both systems, while the related reaction rates have also be obtained from Monte Carlo kinetic simulations. The limitations of the 2-aminopyridine dimer as a model system for the adenine-thymine base pair are discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3464485]
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12.
  • Aidas, Kestutis, et al. (författare)
  • On the performance of quantum chemical methods to predict solvatochromic effects: The case of acrolein in aqueous solution.
  • 2008
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:19, s. 1-194503
  • Tidskriftsartikel (refereegranskat)abstract
    • The performance of the Hartree-Fock method and the three density functionals B3LYP, PBE0, and CAM-B3LYP is compared to results based on the coupled cluster singles and doubles model in predictions of the solvatochromic effects on the vertical n-->pi(*) and pi-->pi(*) electronic excitation energies of acrolein. All electronic structure methods employed the same solvent model, which is based on the combined quantum mechanics/molecular mechanics approach together with a dynamical averaging scheme. In addition to the predicted solvatochromic effects, we have also performed spectroscopic UV measurements of acrolein in vapor phase and aqueous solution. The gas-to-aqueous solution shift of the n-->pi(*) excitation energy is well reproduced by using all density functional methods considered. However, the B3LYP and PBE0 functionals completely fail to describe the pi-->pi(*) electronic transition in solution, whereas the recent CAM-B3LYP functional performs well also in this case. The pi-->pi(*) excitation energy of acrolein in water solution is found to be very dependent on intermolecular induction and nonelectrostatic interactions. The computed excitation energies of acrolein in vacuum and solution compare well to experimental data.
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13.
  • Ajitha, D, et al. (författare)
  • Spin-orbit ab initio study of alkyl halide dissociation via electronic curve crossing
  • 2004
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:12, s. 5761-5766
  • Tidskriftsartikel (refereegranskat)abstract
    • An ab initio study of the role of electronic curve crossing in the photodissociation dynamics of the alkyl halides is presented. Recent experimental studies show that curve crossing plays a deterministic role in deciding the channel of dissociation. Coupled repulsive potential energy curves of the low-lying n-sigma* states are studied including spin-orbit and relativistic effects. Basis set including effect of core correlation is used. Ab initio vertical excitation spectra of CH3I and CF3I are in agreement with the experimental observation. The curve crossing region is around 2.371 Angstrom for CH3I and CF3I. The potential curves of the repulsive excited states have larger slope for CF3I, suggesting a higher velocity and decreased intersystem crossing probability on fluorination. We also report the potential curves and the region of curve crossing for CH3Br and CH3Cl.
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14.
  • Al-Abdalla, A, et al. (författare)
  • Ab initio model potential embedded-cluster study of the ground and lowest excited states of Cr3+ defects in the elpasolites Cs2NaYCl6 and Cs2NaYBr6
  • 1998
  • Ingår i: Journal of Chemical Physics. - : Springer Science and Business Media LLC. - 0021-9606 .- 1089-7690. ; 108, s. 2005-2014
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper we present the results of an ab initio model potential (AIMP) embedded-cluster study of the ground and lowest excited states of Cr3+ defects in the elpasolites Cs2NaYCl6 and Cs2NaYBr6; complete active space SCF (CASSCF) and averaged coupled-pair functional (ACPF) calculations are performed on CrCl63- and CrBr63- clusters embedded in ab initio model potential representations of the surrounding lattices Cs2NaYCl6 and Cs2NaYBr6. The experimental structural data are revisited and some new results are found which differ significantly from those available in the literature. The calculated local structure parameters and electronic transition energies which can be compared to experiments are found to be very good; new structural and spectroscopic results are produced which have been neither measured nor calculated, which are complementary to the available ones, and whose quality is expected to be high as well. In particular, the question of the competition of the excited-state absorptions with the potential vibronic laser emission has been adressed: A considerable overlap between the broad E-2(g) –> (2)A(1g) excited-state absorption and (4)A(2g) <– T-4(2g) emission bands is predicted in both materials, which must result in a reduction in the emission efficiency. Finally, it is shown that the quantum mechanical embedding effects due to the fact that the external Cs+, Na+, Y3+, Cl-, and Br- ions are not point charges, are non-negligible; lacking of these effects must be one of the reasons which make previous Density Functional Theory calculations show significantly larger discrepancies with the available experiments.
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15.
  • Al-Khalili, A, et al. (författare)
  • Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide
  • 2004
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:12, s. 5700-5708
  • Tidskriftsartikel (refereegranskat)abstract
    • Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD.
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16.
  • Alagia, Michele, et al. (författare)
  • Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene : Experiment and theory
  • 2005
  • Ingår i: Journal of chemical physics Online. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 122:12, s. 124305-
  • Tidskriftsartikel (refereegranskat)abstract
    • The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K-edge absorption spectrum present two main groups of discrete transitions between 283 and 288  eV photon energy, due to absorption to * virtual orbitals, and broader structures at higher energy, involving * virtual orbitals. The sharp absorption structures to the * empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K-edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of * symmetry, from the six chemically shifted C 1s core orbitals. ©2005 American Institute of Physics
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17.
  • Aleksis, Rihards, et al. (författare)
  • Low-power synchronous helical pulse sequences for large anisotropic interactions in MAS NMR : Double-quantum excitation of N-14
  • 2020
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 153:24
  • Tidskriftsartikel (refereegranskat)abstract
    • We develop a theoretical framework for a class of pulse sequences in the nuclear magnetic resonance (NMR) of rotating solids, which are applicable to nuclear spins with anisotropic interactions substantially larger than the spinning frequency, under conditions where the radiofrequency amplitude is smaller than or comparable to the spinning frequency. The treatment is based on average Hamiltonian theory and allows us to derive pulse sequences with well-defined relationships between the pulse parameters and spinning frequency for exciting specific coherences without the need for any detailed calculations. This framework is applied to the excitation of double-quantum spectra of N-14 and is used both to evaluate the existing low-power pulse schemes and to predict the new ones, which we present here. It is shown that these sequences can be designed to be gamma -encoded and therefore allow the acquisition of sideband-free spectra. It is also shown how these new double-quantum excitation sequences are incorporated into heteronuclear correlation NMR, such as H-1-N-14 dipolar double-quantum heteronuclear multiple-quantum correlation spectroscopy. The new experiments are evaluated both with numerical simulations and experiments on glycine and N-acetylvaline, which represent cases with moderate and large quadrupolar interactions, respectively. The analyzed pulse sequences perform well for the case of a moderate quadrupolar interaction, however poorly with a large quadrupolar interaction, for which future work on pulse sequence development is necessary.
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18.
  • Aleksis, Rihards, et al. (författare)
  • Separation of quadrupolar and paramagnetic shift interactions in high-resolution nuclear magnetic resonance of spinning powders
  • 2021
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 155:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Separation and correlation of the shift anisotropy and the first-order quadrupolar interaction of spin I = 1 nuclei under magic-angle spinning (MAS) are achieved by the phase-adjusted spinning sideband (PASS) nuclear magnetic resonance (NMR) experiment. Compared to methods for static samples, this approach has the benefit of higher sensitivity and resolution. Moreover, the PASS experiment has the advantage over previous MAS sequences in the ability to completely separate the shift anisotropy and first-order quadrupolar interactions. However, the main drawback of the pulse sequence is the lower excitation bandwidth. The sequence is comprehensively evaluated using theoretical calculations and numerical simulations and applied experimentally to the H-2 NMR of a range of paramagnetic systems: deuterated nickel(II) acetate tetrahydrate, deuterated copper(II) chloride dihydrate, and two forms of deuterated oxyhydride ion conductor BaTiO3-xHy. Our results show that despite the issue with broadband excitation, the extracted shift and quadrupolar interaction tensors and the Euler angles relating the two tensors match well with the NMR parameters obtained with static NMR methods. Therefore, the new application of the PASS experiment is an excellent addition to the arsenal of NMR experiments for H-2 and potentially N-14 in paramagnetic solids.
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19.
  • Alfredsson, Ylvi, et al. (författare)
  • Electronic structure of a vapor-deposited metal-free phthalocyanine thin film
  • 2005
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:21
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.
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20.
  • Allum, Felix, et al. (författare)
  • Coulomb explosion imaging of CH3I and CH2CII photodissociation dynamics
  • 2018
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149:20
  • Tidskriftsartikel (refereegranskat)abstract
    • The photodissociation dynamics of CH3I and CH2CII at 272 nm were investigated by time-resolved Coulomb explosion imaging, with an intense non-resonant 815nmprobe pulse. Fragment ion momenta over a widem/z range were recorded simultaneously by coupling a velocity map imaging spectrometer with a pixel imaging mass spectrometry camera. For both molecules, delay-dependent pump-probe features were assigned to ultraviolet-induced carbon-iodine bond cleavage followed by Coulomb explosion. Multi-mass imaging also allowed the sequential cleavage of both carbon-halogen bonds in CH2ClI to be investigated. Furthermore, delay-dependent relative fragment momenta of a pair of ions were directly determined using recoil-frame covariance analysis. These results are complementary to conventional velocity map imaging experiments and demonstrate the application of time-resolved Coulomb explosion imaging to photoinduced real-time molecular motion.
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21.
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22.
  • Amft, Martin, et al. (författare)
  • Influence of the cluster dimensionality on the binding behavior of CO and O(2) on Au(13)
  • 2012
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:2, s. 024312-
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an ab initio density functional theory study of the binding behavior of CO and O(2) molecules to two-and three-dimensional isomers of Au(13) in order to investigate the potential catalytic activity of this cluster towards low-temperature CO oxidation. First, we scanned the potential energy surface of Au(13) and studied the effect of spin-orbit coupling on the relative stabilities of the 21 isomers we identified. While spin-orbit coupling increases the stability of the three-dimensional more than the two-dimensional isomers, the ground state structure at 0 K remains planar. Second, we systematically studied the binding of CO and O(2) molecules onto the planar and three-dimensional structures lowest in energy. We find that the isomer dimensionality has little effect on the binding of CO to Au(13). O(2), on the other hand, binds significantly to the three-dimensional isomer only. The simultaneous binding of multiple CO molecules decreases the binding energy per molecule. Still, the CO binding remains stronger than the O(2) binding. We did not find a synergetic effect due to the co-adsorption of both molecular species. On the three-dimensional isomer, we find O(2) dissociation to be exothermic with an dissociation barrier of 1.44 eV.
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23.
  • Amini, Kasra, et al. (författare)
  • Alignment, orientation, and Coulomb explosion of difluoroiodobenzene studied with the pixel imaging mass spectrometry (PImMS) camera
  • 2017
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 147:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Laser-induced adiabatic alignment and mixed-field orientation of 2,6-difluoroiodobenzene (C6H3F2I) molecules are probed by Coulomb explosion imaging following either near-infrared strong-field ionization or extreme-ultraviolet multi-photon inner-shell ionization using free-electron laser pulses. The resulting photoelectrons and fragment ions are captured by a double-sided velocity map imaging spectrometer and projected onto two position-sensitive detectors. The ion side of the spectrometer is equipped with a pixel imaging mass spectrometry camera, a time-stamping pixelated detector that can record the hit positions and arrival times of up to four ions per pixel per acquisition cycle. Thus, the time-of-flight trace and ion momentum distributions for all fragments can be recorded simultaneously. We show that we can obtain a high degree of one-and three-dimensional alignment and mixed-field orientation and compare the Coulomb explosion process induced at both wavelengths.
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24.
  • Amira, S., et al. (författare)
  • OD vibrations and hydration structure in an Al3+(aq) solution from a Car-Parrinello molecular-dynamics simulation
  • 2006
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 124:10
  • Tidskriftsartikel (refereegranskat)abstract
    • The optimized geometry, energetics, and vibrational properties of Al(D2O)(n)(3+) clusters, with n=1,2,4, and 6, have been studied using plane waves, different local basis sets, different methodologies [density-functional theory, MP2, CCSD(T)], and different functionals (BLYP, PBE). Moreover, Car-Parrinello molecular-dynamics (MD) simulations using the BLYP functional, plane waves, and the Vanderbilt ultrasoft pseudopotentials have been performed for an aqueous Al3+ solution with 1 ion and 32 D2O molecules in a periodic box at room temperature, studied for 10 ps. The cluster calculations were performed to pinpoint possible shortcomings of the electronic structure description used in the Car-Parinello MD (CPMD) simulation. For the clusters, the hydration structure and interaction energies calculated with the 'BLYP/plane-wave' approach agree well with high-level ab initio methods but the exchange-correlation functional introduces errors in the OD stretching frequencies (both in the absolute values and in the ion-induced shifts). For the aqueous solution, the CPMD simulation yields structural properties in good agreement with experimental data. The CPMD-simulated OD stretching vibrational band for the first-shell water molecules around Al3+ is strongly downshifted by the influence of the ion and is compared with experimental data from the literature. To make such a comparison meaningful, the influences of a number of systematic effects have been addressed, such as the exchange-correlation functional, the fictitious electron mass, anharmonicity effects, and the small box size in the simulation. Each of these factors (except the last one) is found to affect the OD frequency by 100 cm(-1) or more. The final corrected frequencies agree with experiment within similar to 30 cm(-1) for bulk water but are too little downshifted for the first-shell Al3+(aq) water molecules (by similar to 200 cm(-1)).
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25.
  • Andersen, J, et al. (författare)
  • Communication: THz absorption spectrum of the CO2-H2O complex: Observation and assignment of intermolecular van der Waals vibrations.
  • 2014
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Terahertz absorption spectra have been recorded for the weakly bound CO2-H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems' flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point energy of 273 ± 15 cm(-1) from the class of intermolecular van der Waals vibrations is proposed and the combination with high-level quantum chemical calculations provides a value of 726 ± 15 cm(-1) for the dissociation energy D0.
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26.
  • Andersen, J., et al. (författare)
  • Competition between weak OH·π and CH·O hydrogen bonds : THz spectroscopy of the C2H2 - H2O and C2H4 - H2O complexes
  • 2017
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 146:19
  • Tidskriftsartikel (refereegranskat)abstract
    • THz absorption spectra have been recorded for the weakly bound molecular complexes of H2O with C2H4 and C2H2 embedded in cryogenic neon matrices at 2.8 K. The observation and assignment of a large-amplitude acceptor OH librational mode of the C2H2 - H2O complex at 145.5 cm−1 confirms an intermolecular CH⋯O hydrogen-bonded configuration of C2v symmetry with the H2O subunit acting as the hydrogen bond acceptor. The observation and assignment of two large-amplitude donor OH librational modes of the C2H4 - H2O complex at 255.0 and 187.5 cm−1, respectively, confirms an intermolecular OH⋯π hydrogen-bonded configuration with the H2O subunit acting as the hydrogen bond donor to the π-cloud of C2H4. A (semi)-empirical value for the change of vibrational zero-point energy of 4.0-4.1 kJ mol−1 is proposed and the combination with quantum chemical calculations at the CCSD(T)-F12b/aug-cc-pVQZ level provides a reliable estimate of 7.1 ± 0.3 kJ mol−1 for the dissociation energy D0 of the C2H4 - H2O complex. In addition, tentative assignments for the two strongly infrared active OH librational modes of the ternary C2H4 - HOH - C2H4 complex having H2O as a doubly OH·π hydrogen bond donor are proposed at 213.6 and 222.3 cm−1. The present findings demonstrate that the relative stability of the weak hydrogen bond motifs is not entirely rooted in differences of electronic energy but also to a large extent by differences in the vibrational zero-point energy contributions arising from the class of large-amplitude intermolecular modes.
  •  
27.
  • Andersen, J, et al. (författare)
  • Spectroscopic identification of ethanol-water conformers by large-amplitude hydrogen bond librational modes.
  • 2015
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 143:22
  • Tidskriftsartikel (refereegranskat)abstract
    • The far-infrared absorption spectra have been recorded for hydrogen-bonded complexes of water with ethanol embedded in cryogenic neon matrices at 2.8 K. The partial isotopic H/D-substitution of the ethanol subunit enabled by a dual inlet deposition procedure enables the observation and unambiguous assignment of the intermolecular high-frequency out-of-plane and the low-frequency in-plane donor OH librational modes for two different conformations of the mixed binary ethanol/water complex. The resolved donor OH librational bands confirm directly previous experimental evidence that ethanol acts as the O⋯HO hydrogen bond acceptor in the two most stable conformations. In the most stable conformation, the water subunit forces the ethanol molecule into its less stable gauche configuration upon dimerization owing to a cooperative secondary weak O⋯HC hydrogen bond interaction evidenced by a significantly blue-shift of the low-frequency in-plane donor OH librational band origin. The strong correlation between the low-frequency in-plane donor OH librational motion and the secondary intermolecular O⋯HC hydrogen bond is demonstrated by electronic structure calculations. The experimental findings are further supported by CCSD(T)-F12/aug-cc-pVQZ calculations of the conformational energy differences together with second-order vibrational perturbation theory calculations of the large-amplitude donor OH librational band origins.
  •  
28.
  • Andersson, Egil, 1981-, et al. (författare)
  • Core-valence double photoionization of the CS2 molecule
  • 2010
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:9, s. 94305-
  • Tidskriftsartikel (refereegranskat)abstract
    • Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy. (C-) 2010 American Institute of Physics. [doi: 10.1063/1.3469812]
  •  
29.
  • Andersson, L. Mauritz (författare)
  • Quantum dynamics using a discretized coherent state representation : An adaptive phase space method
  • 2001
  • Ingår i: Journal of Chemical Physics. - 0021-9606 .- 1089-7690. ; 115:3, s. 1158-1165
  • Tidskriftsartikel (refereegranskat)abstract
    • We introduce a discretized coherent state representation (DCSR) for quantum dynamics. Expansion of a wave function in the nonorthogonal slightly overcomplete set is made with an identity operator computed using an iterative refinement method. Calculating the inverse of the overlap matrix is not necessary. The result is an accurate and efficient representation, where you only put basis functions in the region of phase space where the wave function is nonvanishing. Compared to traditional spatial grid methods, fewer grid points are needed. The DCSR can be viewed as an application of the Weyl-Heisenberg frame and extends it into a useful computational method. A scheme for fully quantum mechanical propagation is constructed and applied to the realistic problem of highly excited vibration in the heavy diatomic molecule Rb-2. Compared to split-operator propagation in a conventional spatial grid, an order of magnitude longer time steps can be taken and fewer grid points are needed. The computational effort scales linearly with the number of basis functions. Nonreflecting boundary conditions are a natural property of the representation and is illustrated in a model of predissociation.
  •  
30.
  • Andersson, M P, et al. (författare)
  • Surface-induced C–O bond anharmonicity of methoxy adsorbed on Cu(100): Experiments and density-functional theory calculations
  • 2005
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:22, s. 1-224714
  • Tidskriftsartikel (refereegranskat)abstract
    • The anharmonic properties of a surface intermediate, methoxy, adsorbed on Cu(100) are investigated by surface infrared overtone spectroscopy and density-functional-theory electronic structure calculations. The anharmonicity is measured in the zero-coverage limit, and it is observed that the anharmonicity is increased upon adsorption as compared with the free methanol. By combining experiments with calculations we demonstrate that modifications of the anharmonicity of the methoxy species is indeed induced by adsorption onto the copper surface and not by the formation of the methoxy species.
  •  
31.
  • Andersson, Ove, et al. (författare)
  • An ice phase of lowest thermal conductivity
  • 2004
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:20, s. 9612-9617
  • Tidskriftsartikel (refereegranskat)abstract
    • On pressurizing at temperatures near 130 K, hexagonal and cubic ices transform implosively at 0.8–1 GPa. The phase produced on transformation has the lowest thermal conductivity among the known crystalline ices and its value decreases on increase in temperature. An ice phase of similar thermal conductivity is produced also when high-density amorphous ice kept at 1 GPa transforms on slow heating when the temperature reaches ∼155 K. These unusual formation conditions, the density and its distinguished thermal conductivity, all indicate that a distinct crystal phase of ice has been produced.
  •  
32.
  • Andersson, Ove, et al. (författare)
  • Effect of pressure on thermal conductivity and pressure collapse of ice in a polymer-hydrogel and kinetic unfreezing at 1 GPa
  • 2011
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:12, s. 124903-
  • Tidskriftsartikel (refereegranskat)abstract
    • We report a study of aqueous solutions of poly(vinylalcohol) and its hydrogel by thermal conductivity,κ, and specific heat measurements. In particular, we investigate (i) the changes in the solution and the hydrogel at 0.1 MPa observed in the 350-90 K range and of the frozen hydrogel at 130 K observed in the range from 0.1 MPa to 1.3 GPa, and (ii) the nature of the pressure collapse of ice in the frozen hydrogel and kinetic unfreezing on heating of its high density water at 1 GPa. The water component of the polymer solution on cooling either first phase separates and then freezes to hexagonal ice or freezes without phase separation and the dispersed polymer chains freeze-concentrate in nanoscopic and microscopic regions of the grain boundaries and grain junctions of the ice crystals in the frozen state of water in the hydrogel. The change in κ with temperature at 1 bar is reversible with some hysteresis, but not reversible with pressure after compression to 0.8 GPa at 130 K. At high pressures the crystallized state collapses showing features of. and specific heat characteristic of formation of high density amorphous solid water. The pressure of structural collapse is 0.08 GPa higher than that of ice at 130 K. The slowly formed collapsed state shows kinetic unfreezing or glass-liquid transition temperature at 140 K for a time scale of 1 s. Comparison with the change in the properties observed for ice shows that κ decreases when the polymer is added. 
  •  
33.
  • Andersson, Ove, et al. (författare)
  • Nature of the pressure-induced collapse of an ice clathrate by dielectric spectroscopy
  • 2008
  • Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 129:23
  • Tidskriftsartikel (refereegranskat)abstract
    • Collapse of an ice clathrate of type II structure containing tetrahydrofuran as guest molecules has been studied at different pressures by dielectric spectroscopy. The sample was pressurized to 1.3 GPa at 130 K and the resulting collapsed state was pressure cycled. The dielectric relaxation time increases at a progressively rapid rate during pressurizing and then decreases slowly on depressurizing, but the dielectric relaxation time does not reach the value of the original state. With increase in pressure, the limiting high frequency permittivity due to orientation of H2O molecules first increases by about 5% until 0.75 GPa and then decreases slightly until 1 GPa, and finally it increases until ~1.2 GPa. The decrease is attributed to the loss of contribution from the reorientational motion of tetrahydrofuran molecules and the increase to densification as the structure mechanically collapses completely in the 1–1.25 GPa range. The relaxation time of the collapsed state is comparable with that of the high-density amorph formed on pressure collapse of ice.
  •  
34.
  • Andersson, Ove, et al. (författare)
  • Pressure-induced collapse of ice clathrate and hexagonal ice mixtures formed by freezing
  • 2009
  • Ingår i: Journal of Chemical Physics. - : American Institute of Physics Publishing LLC. - 0021-9606 .- 1089-7690. ; 131, s. 114503-114513
  • Tidskriftsartikel (refereegranskat)abstract
    • We report thermal conductivity κ measurements of the pressure-induced collapse of two mixtures of ice and tetrahydrofuran (THF) clathrate hydrate formed by freezing aqueous solutions, THF·23 H2O and THF·20 H2O, one containing twice as much excess water than the other. On pressurizing, κ of the solid mixture first decreases at the onset pressure of 0.8 GPa, as occurs for collapse of pure ice, reaches a local minimum at a pressure of 1.0 GPa, and then increases as occurs for the collapse of the pure clathrate THF·17 H2O. This shows that in the apparently homogeneous mixture, the ice and the clathrate collapse as if the two were in a mechanically mixed state. The manner in which the clathrate aggregate can arrange in the solid indicates that ice occupies the interstitial space in the tightly packed aggregates and H2O molecules belonging to the lattice of one form hydrogen bond with that of the other, a feature that is preserved in their collapsed states. On decompression, the original clathrate is partially recovered in the THF·20 H2O mixture, but the collapsed ice does not transform to the low density amorph. We surmise that on irreversible transformation to the original clathrate, the aggregates expand. Any pressure thus exerted on the small domains of the collapsed ice with a hydrogen bonded interface with the clathrate aggregates could prevent it from transforming to the low density amorph. Measurements of κ are useful in investigating structural collapse of crystals when dilatometry is unable to do so, as κ seems to be more sensitive to pressure-induced changes than the volume.
  •  
35.
  • Andersson, Ove, et al. (författare)
  • Spontaneous transformation of water's high-density amorph and a two-stage crystallization to ice VI at 1 GPa : a dielectric study
  • 2004
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:24, s. 11662-11671
  • Tidskriftsartikel (refereegranskat)abstract
    • Dielectric relaxation spectra of a metastable crystal phase formed on implosive and exothermic transformation of pressure-amorphized hexagonal ice have been measured in situ at 0.97 GPa pressure over a range of temperature. The metastable phase showed no relaxation peak at 130 K and 0.97 GPa. When heated at a fixed pressure of 0.97 GPa, it began to transform at ∼ 145 K exothermally to a phase whose relaxation rate and equilibrium dielectric permittivity increased. A second, but slower exothermic transformation also occurred at ∼ 175 K. After keeping at 213 K, the relaxation rate and equilibrium permittivity reached the known values of these two quantities for ice VI. Thus the metastable phase transformed to ice VI in two stages. It is conjectured that the intermediate phase in this transformation could be ice XII. The rate of transformation is not determined by the reorientational relaxation rate of water molecules in the ices
  •  
36.
  • Andersson, Ove, et al. (författare)
  • Sub-Tg features of glasses formed by cooling glycerol under pressure – Additional incompatibility of vibrational with configurational states in the depressurized, high density glass
  • 2016
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 145
  • Tidskriftsartikel (refereegranskat)abstract
    • The vibrational state of a glass is naturally incompatible with its configurational state, which makes the glass structurally unstable. When a glass is kept at constant temperature, both the vibrational and configurational states of a glass change with time until it becomes metastable (equilibrium) liquid and the two states become compatible. The process, known as structural relaxation, occurs at a progressively higher rate during heating, and the properties of a glass change accordingly. We add to this incompatibility by depressurizing a glass that had been formed by cooling a liquid under a high pressure, p, and then investigate the effects of the added incompatibility by studying thermal conductivity, κ, and the heat capacity per unit volume ρCp of the depressurized glass.We use glycerol for the purpose and study first the changes in the features of κ and of ρCp during glass formation oncooling under a set of different p. We then partially depressurize the glass and study the effect of the p-induced instability on the features of and Cp as the glass is isobarically heated to the liquid state.At a given low p, the glass configuration that was formed by cooling at high-p had a higher κ than the glass configuration that was formed by cooling at a low p. The difference is more when the glass is formed at a higher p and/or is depressurized to a lower p. On heating at a low p, its κ decreases before its glass-liquid transition range is reached. The effect is the opposite of the increase in observed on heating a glass at the same p under which it was formed. It is caused by thermally assisted loss of the added incompatibility of configurational and vibrational states of a high-p formed glass kept at low p. If a glass formed under a low-p is pressurized and then heated under high p, it would show the opposite effect, i.e., its κ would first increase to its high p value before its glass-to-liquid transition range.
  •  
37.
  •  
38.
  • Andersson, Ove (författare)
  • Thermal conductivity of normal and deuterated water, crystalline ice, and amorphous ices
  • 2018
  • Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 149:12
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of deuteration on the thermal conductivity kappa of water, crystalline ice, and amorphous ices was studied using the pressure induced amorphization of hexagonal ice, ice Ih, to obtain the deuterated, D2O, forms of low-density amorphous (LDA), high-density amorphous (HDA), and very-high density amorphous (VHDA) ices. Upon deuteration, kappa of ice Ih decreases between 3% and 4% in the 100-270 K range at ambient pressure, but the effect diminishes on densification at 130 K and vanishes just prior to amorphization near 0.8 GPa. The unusual negative value of the isothermal density rho dependence of kappa for ice Ih, g = (d ln kappa/d ln rho)(T) = -4.4, is less so for deuterated ice: g = -3.8. In the case of the amorphous ices and liquid water, kappa of water decreases by 3.5% upon deuteration at ambient conditions, whereas K of HDA and VHDA ices instead increases by up to 5% for pressures up to 1.2 GPa at 130 K, despite HDA's and VHDA's structural similarities with water. The results are consistent with significant heat transport by librational modes in amorphous ices as well as water, and that deuteration increases phonon-phonon scattering in crystalline ice. Heat transport by librational modes is more pronounced in D2O than in H2O at low temperatures due to a deuteration-induced red-shift of librational mode frequencies. Moreover, the results show that kappa of deuterated LDA ice is 4% larger than that of normal LDA at 130 K, and both forms display an unusual temperature dependence of kappa, which is reminiscent of that for crystals (kappa similar to T (-1)), and a unique negative pressure dependence of kappa, which likely is linked to local-order structural similarities to ice Ih. 
  •  
39.
  • Andersson, Ove, et al. (författare)
  • Time-dependent amorphization of ice at 0.8-0.9 GPa
  • 2004
  • Ingår i: Journal of Chemical Physics. - : AIP. - 0021-9606 .- 1089-7690. ; 121:8, s. 3936-3938
  • Tidskriftsartikel (refereegranskat)abstract
    • Thermal conductivity measurements show that ice continues to amorphize for several days when kept at a fixed pressure p in the 0.79–0.88 GPa range, and fixed temperature T in the 127–130 K range. Thermal conductivity k decreases according to a stretched exponential in time, and its limiting long time value k() varies with p and T. At 0.8 GPa and 128 K, k() remains 2.5 times the value observed for high-density amorph. Consequences of these findings for our understanding of amorphization are discussed.
  •  
40.
  • Andersson, Ove, et al. (författare)
  • Transitions in pressure-amorphized clathrate hydrates akin to those of amorphous ices
  • 2019
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Type II clathrate hydrates (CHs) were studied by thermal and dielectric measurements. All CHs amorphize, or collapse, on pressurization to 1.3 GPa below 135 K. After heating to 160 K at 1 GPa, the stability of the amorphous states increases in a process similar to the gradual high density to very high density amorphous ice (HDA to VHDA) transition. On a subsequent pressure decrease, the amorphized CHs expand partly irreversibly similar to the gradual VHDA to expanded HDA ice transformation. After further heating at 1 GPa, weak transition features appear near the HDA to low density amorphous ice transition. The results suggest that CH nucleation sites vanish on heating to 160 K at 1 GPa and that a sluggish partial phase-separation process commences on further heating. The collapsed CHs show two glass transitions (GTs), GT1 and GT2. GT1 is weakly pressure-dependent, 12 K GPa(-1), with a relaxation time of 0.3 s at 140 K and 1 GPa; it is associated with a weak heat capacity increase of 3.7 J H2O-mol(-1) K-1 in a 18 K range and an activation energy of only 38 kJ mol(-1) at 1 GPa. The corresponding temperature of GT2 is 159 K at 0.4 GPa with a pressure dependence of 36 K GPa(-1); it shows 5.5 times larger heat capacity increase and 4 times higher activation energy than GT1. GT1 is observed also in HDA and VHDA, whereas GT2 occurs just above the crystallization temperature of expanded HDA and only within its similar to 0.2-0.7 GPa stable pressure range.
  •  
41.
  • Andersson, Ove, et al. (författare)
  • Unusual Grüneisen and Bridgman parameters of low-density amorphous ice and their implications on pressure induced amorphization
  • 2005
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 122:12, s. 124710-
  • Tidskriftsartikel (refereegranskat)abstract
    • The low-temperature limiting value of the Grüneisen parameter for low-frequency phonons and the density dependence of the thermal conductivity (Bridgman parameter) of low-density amorphous (LDA) ice, high-density amorphous (HDA) ice, hexagonal ice Ih, and cubic ice Ic were calculated from high-pressure sound velocity and thermal conductivity measurements, yielding negative values for all states except HDA ice. LDA ice is the first amorphous state to exhibit a negative Bridgman parameter, and negative Grüneisen parameters are relatively unusual. Since Ih, Ic, and LDA ice all transform to HDA upon pressurization at low temperatures and share the unusual feature of negative Grüneisen parameters, this seems to be a prerequisite for pressure induced amorphization. We estimate that the Grüneisen parameter increases at the ice Ih to XI transition, and may become positive in ice XI, which indicates that proton-ordered ice XI does not amorphize like ice Ih on pressurization.
  •  
42.
  • Andersson, Stig, 1941, et al. (författare)
  • Excitation and desorption of physisorbed H2 via the 2Σu electron scattering resonance.
  • 2017
  • Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 147, s. 114703-1-114703-11
  • Tidskriftsartikel (refereegranskat)abstract
    • Our high-resolution electron energy-loss measurements concern physisorbed H2 and comprise dif- ferential cross sections for the excitation of the internal H2 modes and the H2-surface bonding mode and their combinations and extend over the electron impact energy range of the classical low-energy H2 2Σu resonance. Comparison with corresponding data for the excitation of the internal modes of gas phase H2 reveals that strong elastic electron reflectivity from the Cu(100) substrate profoundly distorts the inelastic scattering pattern for physisorbed H2. We find that this influence can be corrected for and that the resulting peak cross sections agree with the H2 gas phase data, in accordance with theoretical predictions for the excitation of the internal H2 vibration. We have used corrected cross sections for the rotational mode spectra of physisorbed H2, HD, and D2 in a model concerning elec- tron induced desorption via rotation-translation energy conversion. These spectra include transitions from the ground state as well as excited levels of the physisorption potential well. H2 and HD can desorb from all levels while D2, for energetic reason, can only desorb from the excited levels. This model gives a satisfactory account of the observed desorption cross sections and predicts character- istic velocity distributions of the desorbing molecules. The cross section data for H2 and HD reveals that direct bound-free transitions also contribute to the electron induced desorption. 
  •  
43.
  • Andersson, Tomas, et al. (författare)
  • Plasmon single- and multi-quantum excitation in free metal clusters as seen by photoelectron spectroscopy
  • 2011
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:9, s. 094511-
  • Tidskriftsartikel (refereegranskat)abstract
    • Plasmons are investigated in free nanoscale Na, Mg, and K metal clusters using synchrotron radiation-based x-ray photoelectron spectroscopy. The core levels for which the response from bulk and surface atoms can be resolved are probed over an extended binding energy range to include the plasmon loss features. In all species the features due to fundamental plasmons are identified, and in Na and K also those due to either the first order plasmon overtones or sequential plasmon excitation are observed. These features are discussed in view of earlier results for planar macroscopic samples and free clusters of the same materials.
  •  
44.
  • Andersson, T., et al. (författare)
  • Selective adsorption, bound states, and potential parameters for He, Ne, and Ar interacting with a Cu(110) surface
  • 2006
  • Ingår i: J. Chem. Phys.. - : AIP Publishing. - 0021-9606. ; 124
  • Tidskriftsartikel (refereegranskat)abstract
    • Using nozzle beams of He, Ne, and Ar, we have measured diffractive selective adsorption resonances from a Cu(110) surface kept at 20 K. Bound state energies of the atom-surface potentials have been determined from plots of the measured resonance energies versus incident angle and their fits to calculated kinematical dispersion relations. For 3He and 4He we have found a unique level assignment that is compatible with a single gas-surface potential curve with a well depth of 6.05 meV of the He–Cu(110) potential. This value is about 10% larger than the prediction of 5.55 meV from the current physisorption theory. The Ne and Ar data reveal a large number of closely spaced levels with level separations and estimated van der Waals coefficients that are compatible with available theoretical data.
  •  
45.
  • Andersson, Tomas, et al. (författare)
  • The electronic structure of free aluminum clusters: Metallicity and plasmons
  • 2012
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:20
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structure of free aluminum clusters with similar to 3-4 nm radius has been investigated using synchrotron radiation-based photoelectron and Auger electron spectroscopy. A beam of free clusters has been produced using a gas-aggregation source. The 2p core level and the valence band have been probed. Photoelectron energy-loss features corresponding to both bulk and surface plasmon excitation following photoionization of the 2p level have been observed, and the excitation energies have been derived. In contrast to some expectations, the loss features have been detected at energies very close to those of the macroscopic solid. The results are discussed from the point of view of metallic properties in nanoparticles with a finite number of constituent atoms. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4718362]
  •  
46.
  • Andrews, L, et al. (författare)
  • Infrared spectra of cis and trans-(NO)(2)(-) anions in solid argon
  • 1998
  • Ingår i: Journal of Chemical Physics. - 1089-7690 .- 0021-9606. ; 109:1, s. 177-185
  • Tidskriftsartikel (refereegranskat)abstract
    • Laser-ablation of over 20 different metal targets with concurrent 10 K codeposition of Ar/NO mixtures produces metal independent infrared bands at 1589.3 cm−1 due to (NO)2+, a new absorption at 1221.0 cm−1, and a band set at 1300.3, 1222.7, 884.4 cm−1. The latter bands decrease more on annealing than the 1221.0 cm−1 band. Isotopic substitution (14NO,15NO, 15N18O, and mixtures) shows that these new vibrations involve two equivalent N–O oscillators, which identifies two new (NO)2 species. The excellent agreement with frequencies, intensities, and isotopic frequency ratios from density functional theory calculations substantiates assignment of the 1221.0 cm−1 band to trans-(NO)2− and the three band set to cis-(NO)2−. The observation of a weak combination band at 2492.0 cm−1 further substantiates assignment of the two N–O stretching modes in cis-(NO)2−
  •  
47.
  •  
48.
  • Antipov, Sergey V., 1986, et al. (författare)
  • Rate coefficient of CN formation through radiative association: A theoretical study of quantum effects
  • 2009
  • Ingår i: J. Chem. Phys.. - : AIP Publishing. ; 131
  • Tidskriftsartikel (refereegranskat)abstract
    • Radiative association of CN is simulated using a quantum dynamical as well as a semiclassical approach. A comparison of the resulting energy-resolved cross sections reveals striking quantum effects that are due to shape resonances. These, in turn, arise because of states that are quasibound by the centrifugal barrier. The quantal rate coefficient for temperatures from 40 to 1900 K has been computed using the Breit–Wigner theory to account for the resonances. Comparison with the results obtained by Singh and Andreazza [ Astrophys. J. 537, 261 (2000) ] shows that the semiclassical method, which completely omits the shape resonances, is accurate to within 25% above room temperature. At lower temperatures the contribution from the shape resonances to the radiative association rate is more significant.
  •  
49.
  • Antipov, Sergey V., 1986, et al. (författare)
  • Spin-orbit and rotational couplings in radiative association of C((3)P) and N((4)S) atoms.
  • 2011
  • Ingår i: The Journal of chemical physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 135:18
  • Tidskriftsartikel (refereegranskat)abstract
    • The role of spin-orbit and rotational couplings in radiative association of C((3)P) and N((4)S) atoms is investigated. Couplings among doublet electronic states of the CN radical are considered, giving rise to a 6-state model of the process. The solution of the dynamical problem is based on the L(2) method, where a complex absorbing potential is added to the Hamiltonian operator in order to treat continuum and bound levels in the same manner. Comparison of the energy-dependent rate coefficients calculated with and without spin-orbit and rotational couplings shows that the couplings have a strong effect on the resonance structure and low-energy baseline of the rate coefficient.
  •  
50.
  • Antonijevic, Sasa, et al. (författare)
  • Study of water dynamics and distances in paramagnetic solids by variable-temperature two-dimensional H-2 NMR spectroscopy
  • 2007
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A recently proposed two-dimensional H-2 NMR experiment is used to measure the H-2 (spin I=1) quadrupolar and paramagnetic shift anisotropy interactions in powdered CuCl2 center dot 2D(2)O as a function of temperature. The principal components of the quadrupolar and paramagnetic shift anisotropy tensors and the Euler angles describing the orientations of the tensors in the molecular frame are determined at each temperature. For this purpose an analytical approach is introduced to extract desired parameters from motionally averaged two-dimensional line shapes where the averaging is introduced by rapid 180 degrees flips around C-2 axes of D2O molecules. This approach can be readily applied to study various materials containing water of crystallization. It is also clearly shown that the rapid continuous rotation of D2O molecules around their C-2 axes is not taking place in the studied solid in the range of temperatures between 209 and 344 K. Once the paramagnetic shift anisotropy of a deuterium atom is measured accurately it is used to estimate the distance between deuterium and the nearest copper atom bearing an unpaired electron. Excellent agreement is found between structural parameters obtained in this study and those provided by neutron and x-ray diffraction, showing that the paramagnetic shift anisotropy is a sensitive probe of distances in paramagnetic solids. (c) 2007 American Institute of Physics.
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