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• 1.
University of Texas, Physics Department.
University of Texas, Physics Department. Department of Chemistry, University of Gothenburg.
Collision-induced absorption at wavelengths near 5 μm by dense hydrogen gas2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, no 18, article id 181102Article in journal (Refereed)

Based on a recent ab initiointeraction-induced dipole surface of collisionally interacting molecular hydrogen pairs H2–H2, we compute the binary absorption coefficients at wavelengths near 5 μm 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 initiointeraction-induced dipole surface that was inadequate for the 5 μm band.

• 2.
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Diffusion and reaction pathways of water near fully hydrated TiO2 surfaces from ab initio molecular dynamics2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 2, article id 024704Article in journal (Refereed)

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.

• 3.
Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
Universidade Federal de São Carlos, Brazil. Linnaeus University, Faculty of Health and Life Sciences, Department of Chemistry and Biomedical Sciences.
Computer simulations of alkali-acetate solutions: Accuracy of the forcefields in difference concentrations2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, p. 1-10, article id 194102Article in journal (Refereed)

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.

Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 17, p. 174702-Article in journal (Refereed)

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. (C) 2014 AIP Publishing LLC.

• 5.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 17, p. 174702-Article in journal (Refereed)

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.

Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 8, p. 084705-Article in journal (Refereed)

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.

• 7.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
Molecular layers of ZnPc and FePc on Au(111) surface: Charge transfer and chemical interaction2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 8, p. 084705-Article in journal (Refereed)

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.

• 8.
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512). KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512).
Ultrafast deactivation processes in the 2-aminopyridine dimer and the adenine-thymine base pair: Similarities and differences2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 6, p. 064302-Article in journal (Refereed)

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]

• 9. Ajitha, D
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Physical and Analytical Chemistry, Quantum Chemistry.
Spin-orbit ab initio study of alkyl halide dissociation via electronic curve crossing2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 12, p. 5761-5766Article in journal (Refereed)

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.

• 10. Al-Abdalla, A
Department of Theoretical Chemistry, Lund University.
Ab initio model potential embedded-cluster study of the ground and lowest excited states of Cr3+ defects in the elpasolites Cs2NaYCl6 and Cs2NaYBr61998In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 108, p. 2005-2014Article in journal (Refereed)

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.

• 11.
Department of Physics, Uppsala University.
KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512). Department of Physics, Uppsala University. Department of Physics, Uppsala University. MAX-lab, University of Lund. KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512). KTH, School of Biotechnology (BIO), Theoretical Chemistry (closed 20110512). Department of Physics, Uppsala University. Department of Physics, Uppsala University. Department of Physics, Uppsala University. Department of Physics, Uppsala University.
Electronic structure of a vapor-deposited metal-free phthalocyanine thin film2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 21Article in journal (Refereed)

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.

• 12.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Electronic structure of a vapor-deposited metal-free phthalocyanine thin film2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 21, p. 214723-Article in journal (Refereed)

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 N1sXAS 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.

• 13. Al-Khalili, A
KTH, Superseded Departments, Physics.
Dissociative recombination cross section and branching ratios of protonated dimethyl disulfide and N-methylacetamide2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 12, p. 5700-5708Article in journal (Refereed)

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.

• 14.
Univ Oxford, Chem Res Lab, Dept Chem, Oxford OX1 3TA, England.
Univ Oxford, Chem Res Lab, Dept Chem, Oxford OX1 3TA, England. Univ Oxford, Chem Res Lab, Dept Chem, Oxford OX1 3TA, England. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany. Univ Oxford, Chem Res Lab, Dept Chem, Oxford OX1 3TA, England. St Petersburg State Univ, 7-9 Univ Skaya Nab, St Petersburg 199034, Russia. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany. Max Born Inst, Max Born Str 2A, D-12489 Berlin, Germany. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany. Univ Paris Saclay, LIDYL, CEA, CNRS,CEA Saclay, F-91191 Gif Sur Yvette, France. Univ Paris Saclay, LIDYL, CEA, CNRS,CEA Saclay, F-91191 Gif Sur Yvette, France. Univ Oxford, Phys & Theoret Chem Lab, Dept Chem, Oxford OX1 3QZ, England. Max Born Inst, Max Born Str 2A, D-12489 Berlin, Germany. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Daresbury Lab, Warrington WA4 4AD, Cheshire, England. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Lund Univ, Dept Phys, S-22100 Lund, Sweden. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Deutsch Elektronen Synchrotron DESY, Ctr Free Electron Laser Sci, Notkestr 85, D-22607 Hamburg, Germany;Univ Hamburg, Ctr Ultrafast Imaging, Luruper Chaussee 149, D-22761 Hamburg, Germany;Univ Hamburg, Dept Phys, Luruper Chaussee 149, D-22761 Hamburg, Germany;Univ Hamburg, Dept Chem, Martin Luther King Pl 6, D-20146 Hamburg, Germany. Lund Univ, Dept Phys, S-22100 Lund, Sweden. Univ Oxford, Chem Res Lab, Dept Chem, Oxford OX1 3TA, England. Lund Univ, Dept Phys, S-22100 Lund, Sweden. Univ Oxford, Phys & Theoret Chem Lab, Dept Chem, Oxford OX1 3QZ, England. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany. St Petersburg State Univ, 7-9 Univ Skaya Nab, St Petersburg 199034, Russia. Univ Oxford, Chem Res Lab, Dept Chem, Oxford OX1 3TA, England. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany;European XFEL, Holzkoppel 4, D-22869 Schenefeld, Germany. Max Born Inst, Max Born Str 2A, D-12489 Berlin, Germany. Univ Paris Saclay, LIDYL, CEA, CNRS,CEA Saclay, F-91191 Gif Sur Yvette, France. Kansas State Univ, Dept Phys, JR Macdonald Lab, Manhattan, KS 66506 USA. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany. Aarhus Univ, Dept Chem, Langelandsgade 140, DK-8000 Aarhus C, Denmark. Deutsch Elektronen Synchrotron DESY, Notkestr 85, D-22607 Hamburg, Germany;Max Planck Inst Biophys Chem, D-37077 Gottingen, Germany;Univ Gottingen, Inst Xray Phys, D-37077 Gottingen, Germany. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Deutsch Elektronen Synchrotron DESY, Ctr Free Electron Laser Sci, Notkestr 85, D-22607 Hamburg, Germany;Univ Hamburg, Ctr Ultrafast Imaging, Luruper Chaussee 149, D-22761 Hamburg, Germany. UCL, Dept Phys & Astron, London WC1E 6BT, England. Univ Oxford, Chem Res Lab, Dept Chem, Oxford OX1 3TA, England. Deutsch Elektronen Synchrotron DESY, Ctr Free Electron Laser Sci, Notkestr 85, D-22607 Hamburg, Germany;Univ Hamburg, Dept Chem, Martin Luther King Pl 6, D-20146 Hamburg, Germany. Kansas State Univ, Dept Phys, JR Macdonald Lab, Manhattan, KS 66506 USA. Univ Oxford, Chem Res Lab, Dept Chem, Oxford OX1 3TA, England. Sorbonne Univ, LCPMR, CNRS, F-75005 Paris, France. Kansas State Univ, Dept Phys, JR Macdonald Lab, Manhattan, KS 66506 USA.
Coulomb explosion imaging of CH3I and CH2CII photodissociation dynamics2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 20, article id 204313Article in journal (Refereed)

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.

• 15. Amft, Martin
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
Influence of the cluster dimensionality on the binding behavior of CO and O(2) on Au(13)2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 2, p. 024312-Article in journal (Refereed)

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.

• 16.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Influence of the cluster dimensionality on the binding behavior of CO and O(2) on Au(13)2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 2, p. 024312-Article in journal (Refereed)

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.

• 17. Amira, S.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
OD vibrations and hydration structure in an Al3+(aq) solution from a Car-Parrinello molecular-dynamics simulation2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 10Article in journal (Refereed)

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)).

• 18.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry. Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
OD vibrations and hydration structure in an Al3+(aq) solution from a Car-Parrinello Molecular Dynamics Simulation2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 10, p. 104501-Article in journal (Refereed)

The optimized geometry, energetics, and vibrational properties of Al(D2O) 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 ~30 cm–1 for bulk water but are too little downshifted for the first-shell Al3+(aq) water molecules (by ~200 cm–1).

Stockholm University, Faculty of Science, Department of Physics.
Core-valence double photoionization of the CS2 molecule2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 9, p. 94305-Article in journal (Refereed)

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]

KTH, School of Biotechnology (BIO), Theoretical Chemistry. KTH, School of Biotechnology (BIO), Theoretical Chemistry.
Core-valence double photoionization of the CS2 molecule2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 9, p. 094305-Article in journal (Refereed)

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.

• 21.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
Core-valence double photoionization of the CS2 molecule2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 9, p. 094305-Article in journal (Refereed)

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.

Quantum dynamics using a discretized coherent state representation: An adaptive phase space method2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 115, no 3, p. 1158-1165Article in journal (Refereed)

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.

• 23.
Umeå University, Faculty of Science and Technology, Department of Physics.
Thermal conductivity of normal and deuterated water, crystalline ice, and amorphous ices2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 149, no 12, article id 124506Article in journal (Refereed)

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.

• 24.
Umeå University, Faculty of Science and Technology, Department of Physics.
Umeå University, Faculty of Science and Technology, Department of Physics.
Transitions in pressure-amorphized clathrate hydrates akin to those of amorphous ices2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 1, article id 014502Article in journal (Refereed)

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.

Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
Transitions in pressure-amorphized clathrate hydrates akin to those of amorphous ices2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 151, no 1, article id 014502Article in journal (Refereed)

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.

• 26.
Umeå University, Faculty of Science and Technology, Department of Physics.
Unusual Grüneisen and Bridgman parameters of low-density amorphous ice and their implications on pressure induced amorphization2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 12, p. 124710-Article in journal (Refereed)

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.

• 27.
Umeå University, Faculty of Science and Technology, Department of Physics.
Sub-Tg features of glasses formed by cooling glycerol under pressure – Additional incompatibility of vibrational with configurational states in the depressurized, high density glass2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, article id 204506Article in journal (Refereed)

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.

• 28.
Umeå University, Faculty of Science and Technology, Department of Physics.
Effect of pressure on thermal conductivity and pressure collapse of ice in a polymer-hydrogel and kinetic unfreezing at 1 GPa2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 12, p. 124903-Article in journal (Refereed)

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.

• 29.
Umeå University, Faculty of Science and Technology, Physics. Umeå University, Faculty of Science and Technology, Physics.
Nature of the pressure-induced collapse of an ice clathrate by dielectric spectroscopy2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, p. 234505-Article in journal (Refereed)

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.

• 30.
Umeå University, Faculty of Science and Technology, Department of Physics.
Department of Materials Science and Engineering, McMaster University, Hamilton, Canada.
Pressure-induced collapse of ice clathrate and hexagonal ice mixtures formed by freezing2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, p. 114503-114513Article in journal (Refereed)

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.

• 31.
Umeå University, Faculty of Science and Technology, Department of Physics.
Spontaneous transformation of water's high-density amorph and a two-stage crystallization to ice VI at 1 GPa: a dielectric study2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 120, no 24, p. 11662-11671Article in journal (Refereed)

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

• 32.
Umeå University, Faculty of Science and Technology, Department of Physics.
Department of Materials Science and Engineering, McMaster University, Hamilton, Ontario, Canada.
Thermal conductivity of Glycerol’s liquid, glass, and crystal states, glass-liquid-glass transition, and crystallization at high pressures2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, article id 064504Article in journal (Refereed)
• 33.
Umeå University, Faculty of Science and Technology, Department of Physics.
Time-dependent amorphization of ice at 0.8-0.9 GPa2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 8, p. 3936-3938Article in journal (Refereed)

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($\infty$) varies with p and T. At 0.8 GPa and 128 K, k($\infty$) remains 2.5 times the value observed for high-density amorph. Consequences of these findings for our understanding of amorphization are discussed.

• 34.
Umeå University, Faculty of Science and Technology, Department of Physics.
An ice phase of lowest thermal conductivity2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 120, no 20, p. 9612-9617Article in journal (Refereed)

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.

• 35.
Göteborgs Universitet.
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics.
Excitation and desorption of physisorbed H2 via the 2Σu electron scattering resonance.2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, p. 114703-1-114703-11, article id 114703Article in journal (Refereed)

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.

• 36.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
Plasmon single- and multi-quantum excitation in free metal clusters as seen by photoelectron spectroscopy2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 134, no 9, p. 094511-Article in journal (Refereed)

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.

• 37.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Surface and Interface Science.
The electronic structure of free aluminum clusters: Metallicity and plasmons2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 20, p. 204504-Article in journal (Refereed)

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.

• 38.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
Rate constants and branching ratios for the dissociative recombination of C3D7+ and C4D9+2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Article in journal (Refereed)
• 39.
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
Isotopic investigation of the transport of oxygen species in Y-stabilized zirconiaIn: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Article in journal (Other academic)
• 40.
Department of Chemistry and Molecular Biology, University of Gothenburg.
Department of Chemistry, University of Gothenburg. Department of Chemistry and Molecular Biology, University of Gothenburg.
Spin-orbit and rotational couplings in radiative association of C(3P) and N(4S) atoms2011In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 135, no 18, article id 184302Article in journal (Refereed)

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 L2 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.

• 41.
Department of Chemistry and Molecular Biology, University of Gothenburg.
Department of Chemistry, University of Gothenburg. Department of Chemistry and Molecular Biology, University of Gothenburg. Department of Chemistry, University of Gothenburg.
Rate coefficient of CN formation through radiative association: A theoretical study of quantum effects2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 131, no 7, article id 74302Article in journal (Refereed)

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.

• 42. Antzutkin, Oleg
Stockholm University. Stockholm University. Stockholm University.
Suppression of sidebands in magic-angle-spinning nuclear magnetic resonance: general principles and analytical solutions1994In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 100, no 1, p. 130-140Article in journal (Refereed)

Several theoretical and experimental aspects of sideband suppression in the nuclear magnetic resonance (NMR) spectra of rotating solids are considered. The principles of sideband suppression are explored using general symmetry arguments and previous treatments are examined critically. Analytical solutions are given for sideband suppression pulse sequences employing four, five, six, and nine pulses. The analytical solutions for four pulses are complete. Experimental demonstrations are given. The Journal of Chemical Physics is copyrighted by The American Institute of Physics.

• 43.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
National Institutes of Health.
High-order multiple quantum excitation in 13C nuclear magnetic resonance spectroscopy of organic solids1999In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 110, no 6, p. 2749-2752Article in journal (Refereed)

Excitation and detection of high-order multiple quantum (MQ) coherences among 13C nuclear spins in singly-13C-labeled organic solids is demonstrated experimentally. MQ signals involving at least ten quanta of spin angular momentum are observed in nuclear magnetic resonance (NMR) measurements on polycrystalline L-methionine-methyl-13C and L-alanine-1-13C, using a time-reversible multiple pulse excitation sequence modified specifically for experiments on systems with weak homonuclear dipole-dipole couplings and strong inhomogeneous interactions such as anisotropic chemical shifts. The feasibility of high-order MQ excitation and detection in 13C-labeled organic solids promises to expand significantly the range of applications of MQ NMR as a structural tool, to include such systems as 13C-labeled synthetic polymers and biopolymers.

• 44. Aquilante, Francesco
A theoretical investigation of valence and Rydberg electronic states of acrolein.2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 23, p. 12323-12334Article in journal (Refereed)

The main features of the ultraviolet spectrum of acrolein have been studied by a multireference perturbative treatment and by a time dependent density functional approach. The valence and Rydberg transition energies have been calculated and the assignment of the experimental bands has been clarified. The different relaxation trends of the three lowest singlet and triplet excited states have been analyzed by unconstrained geometry optimizations. This has allowed, in particular, the characterization of a twisted (3)(pipi*) state, which is crucial for the interesting photophysics and photochemistry of the acrolein molecule and, more generally, of the alpha,beta-enones. Solvatochromic shifts in aqueous solution have been investigated using a combined discrete/continuum approach based on the so called polarizable continuum model. The experimental trends are well reproduced by this approach and a closer degeneracy in the triplet manifold has been detected in solution with respect to gas phase.

• 45. Aquilante, Francesco
Department of Theoretical Chemistry, Lund University.
Atomic Cholesky decompositions: A route to unbiased auxiliary basis sets for density fitting approximation with tunable accuracy and efficiency2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, p. 154107-Article in journal (Refereed)

Cholesky decomposition of the atomic two-electron integral matrix has recently been proposed as a procedure for automated generation of auxiliary basis sets for the density fitting approximation [F. Aquilante , J. Chem. Phys. 127, 114107 (2007)]. In order to increase computational performance while maintaining accuracy, we propose here to reduce the number of primitive Gaussian functions of the contracted auxiliary basis functions by means of a second Cholesky decomposition. Test calculations show that this procedure is most beneficial in conjunction with highly contracted atomic orbital basis sets such as atomic natural orbitals, and that the error resulting from the second decomposition is negligible. We also demonstrate theoretically as well as computationally that the locality of the fitting coefficients can be controlled by means of the decomposition threshold even with the long-ranged Coulomb metric. Cholesky decomposition-based auxiliary basis sets are thus ideally suited for local density fitting approximations.

• 46. Aquilante, Francesco
Department of Theoretical Chemistry, Lund University.
Analytic derivatives for the Cholesky representation of the two-electron integrals2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 3, p. 034106-Article in journal (Refereed)

We propose a formalism for calculating analytic derivatives of the electronic energy with respect to nuclear coordinates using Cholesky decomposition of the two-electron integrals. The formalism is derived by exploiting the equivalence of Cholesky decomposition and density fitting when a suitable auxiliary basis set is used for expanding atomic orbital product densities in the latter. An implementation of gradients at the nonhybrid density functional theory level is presented, and sample calculations demonstrate that the errors in equilibrium geometries due to the Cholesky representation of the integrals can be controlled by adjusting the decomposition threshold.

• 47. Aquilante, Francesco
Department of Theoretical Chemistry, Lund University.
Unbiased auxiliary basis sets for accurate two-electron integral approximations2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 127, no 11, p. 114107-Article in journal (Refereed)

We propose Cholesky decomposition (CD) of the atomic two-electron integral matrix as a robust and general technique for generating auxiliary basis sets for the density fitting approximation. The atomic CD (aCD) auxiliary basis set is calculated on the fly and is not biased toward a particular quantum chemical method. Moreover, the accuracy of the aCD basis set can be controlled with a single parameter.

• 48. Aquilante, Francesco
Department of Theoretical Chemistry, Lund University.
Low-cost evaluation of the exchange Fock matrix from Cholesky and density fitting representations of the electron repulsion integrals2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 126, no 19, p. 194106-Article in journal (Refereed)

The authors propose a new algorithm, “local K” (LK), for fast evaluation of the exchange Fock matrix in case the Cholesky decomposition of the electron repulsion integrals is used. The novelty lies in the fact that rigorous upper bounds to the contribution from each occupied orbital to the exchange Fock matrix are employed. By formulating these inequalities in terms of localized orbitals, the scaling of computing the exchange Fock matrix is reduced from quartic to quadratic with only negligible prescreening overhead and strict error control. Compared to the unscreened Cholesky algorithm, the computational saving is substantial for systems of medium and large sizes. By virtue of its general formulation, the LK algorithm can be used also within the class of methods that employ auxiliary basis set expansions for representing the electron repulsion integrals.

• 49. Aquilante, Francesco
Department of Theoretical Chemistry, Lund University.
Accurate ab initio density fitting for multiconfigurational self-consistent field methods2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 2, p. 024113-Article in journal (Refereed)

Using Cholesky decomposition and density fitting to approximate the electron repulsion integrals, an implementation of the complete active space self-consistent field (CASSCF) method suitable for large-scale applications is presented. Sample calculations on benzene, diaquo-tetra-mu-acetato-dicopper(II), and diuraniumendofullerene demonstrate that the Cholesky and density fitting approximations allow larger basis sets and larger systems to be treated at the CASSCF level of theory with controllable accuracy. While strict error control is an inherent property of the Cholesky approximation, errors arising from the density fitting approach are managed by using a recently proposed class of auxiliary basis sets constructed from Cholesky decomposition of the atomic electron repulsion integrals.

• 50. Aquilante, Francesco
Fast noniterative orbital localization for large molecules.2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, no 17Article in journal (Refereed)

We use Cholesky decomposition of the density matrix in atomic orbital basis to define a new set of occupied molecular orbital coefficients. Analysis of the resulting orbitals (”Cholesky molecular orbitals”) demonstrates their localized character inherited from the sparsity of the density matrix. Comparison with the results of traditional iterative localization schemes shows minor differences with respect to a number of suitable measures of locality, particularly the scaling with system size of orbital pair domains used in local correlation methods. The Cholesky procedure for generating orthonormal localized orbitals is noniterative and may be made linear scaling. Although our present implementation scales cubically, the algorithm is significantly faster than any of the conventional localization schemes. In addition, since this approach does not require starting orbitals, it will be useful in local correlation treatments on top of diagonalization-free Hartree-Fock optimization algorithms.

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