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  • 1.
    Abel, Martin
    et al.
    University of Texas, Physics Department.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Gustafsson, Magnus
    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)
    Abstract [en]

    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.
    Antipov, Sergey V.
    et al.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Gustafsson, Magnus
    Department of Chemistry, University of Gothenburg.
    Nyman, Gunnar
    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)
    Abstract [en]

    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.

  • 3.
    Antipov, Sergey V.
    et al.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Sjölander, Tobias
    Department of Chemistry, University of Gothenburg.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Gustafsson, Magnus
    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)
    Abstract [en]

    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.

  • 4. Antzutkin, Oleg
    et al.
    Song, Zhiyang
    Stockholm University.
    Feng, Xiaolong
    Stockholm University.
    Levitt, Malcolm H.
    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)
    Abstract [en]

    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.

  • 5.
    Antzutkin, Oleg
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Tycko, Robert
    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)
    Abstract [en]

    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.

  • 6. Arvantidis, J.
    et al.
    Meletov, K.P.
    Papagelis, K.
    Ves, S.
    Kourouklis, G. A.
    Soldatov, Alexander
    Prassides, K.
    Raman modes of the two-dimensional tetragonal polymeric phase of C60 under high pressure2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 114, no 20, p. 9099-9104Article in journal (Refereed)
    Abstract [en]

    The effect of high hydrostatic pressure, up to 12 GPa, on the phonon spectrum and the material stability of the two-dimensional (2D) tetragonal C60 polymer have been studied by means of Raman spectroscopy in the frequency range 100-2000 cm-1. A number of Raman modes appear in the spectrum for pressures above ~1.4 GPa, whose intensities increase with pressure. The pressure coefficients of the majority of the phonon modes change gradually to lower values for pressures around 4.0 GPa. The deformation of the C60 molecular cage along with the change of the material to a more isotropic state (as far as its elastic properties are concerned) resulting from the application of high pressure may be causing the observed effects in the Raman spectra. These effects are reversible upon pressure release and therefore the material is stable in the pressure region investigated.

  • 7.
    Avakyan, Leon
    et al.
    Department of Physics and I3N, University of Aveiro, Aveiro, Portugal.
    Paramonova, Ekaterina
    Institute of Mathematical Problems of Biology, Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, 142290 Moscow Region, Russian Federation.
    Coutinho, José
    Department of Physics and I3N, University of Aveiro, Aveiro, Portugal.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bystrov, Vladimir
    Institute of Mathematical Problems of Biology, Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, 142290 Moscow Region, Russian Federation.
    Bugaev, Lusegen
    Physics Faculty, Southern Federal University, Rostov-on-Don 344090, Russian Federation.
    Optoelectronics and defect levels in hydroxyapatite by first-principles2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, no 15, article id 154706Article in journal (Refereed)
    Abstract [en]

    Hydroxyapatite (HAp) is an important component of mammal bones and teeth, being widely used in prosthetic implants. Despite the importance of HAp in medicine, several promising applications involving this material (e.g., in photo-catalysis) depend on how well we understand its fundamental properties. Among the ones that are either unknown or not known accurately, we have the electronic band structure and all that relates to it, including the bandgap width. We employ state-of-the-art methodologies, including density hybrid-functional theory and many-body perturbation theory within the dynamically screened single-particle Green's function approximation, to look at the optoelectronic properties of HAp. These methods are also applied to the calculation of defect levels. We find that the use of a mix of (semi-)local and exact exchange in the exchange-correlation functional brings a drastic improvement to the band structure. Important side effects include improvements in the description of dielectric and optical properties not only involving conduction band (excited) states but also the valence. We find that the highly dispersive conduction band bottom of HAp originates from anti-bonding σ* states along the ⋯OH-OH-⋯ infinite chain, suggesting the formation of a conductive 1D-ice phase. The choice of the exchange-correlation treatment to the calculation of defect levels was also investigated by using the OH-vacancy as a testing model. We find that donor and acceptor transitions obtained within semi-local density functional theory (DFT) differ from those of hybrid-DFT by almost 2 eV. Such a large discrepancy emphasizes the importance of using a high-quality description of the electron-electron interactions in the calculation of electronic and optical transitions of defects in HAp.

  • 8.
    Buser, Michael
    et al.
    University of Texas, Physics Department.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Gustafsson, Magnus
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Moraldi, Massimo
    Dipartimento di Fisica, Universitá di Firenze and INFM, Unitá di Firenze.
    Champagne, Mark H.
    Department of Chemistry, Michigan State University.
    Hunt, Katherine L.C.
    Department of Chemistry, Michigan State University.
    Far-infrared absorption by collisionally interacting nitrogen and methane molecules2004In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 6, p. 2616-2621Article in journal (Refereed)
    Abstract [en]

    Quantum line shape calculations of the rototranslational enhancement spectra of nitrogen-methane gaseous mixtures are reported. The calculations are based on a recent theoretical dipole function for interactingN2 and CH4 molecules, which accounts for the long-range induction mechanisms: multipolar inductions and dispersion force-induced dipoles. Multipolar induction alone was often found to approximate the actual dipole surfaces of pairs of interacting linear molecules reasonably well. However, in the case of the N2-CH4 pair, the absorption spectra calculated with such a dipole function still show a substantial intensity defect at the high frequencies (>250 cm−1) when compared to existing measurements at temperatures from 126 to 297 K, much as was previously reported.

  • 9. Genovese, L.
    et al.
    Neelov, A.
    Goedecker, S.
    Deutsch, T.
    Ghasemi, S. A.
    Willand, A.
    Caliste, D.
    Zilberberg, O.
    Rayson, Mark
    Bergman, A.
    Schneider, R.
    Daubechies wavelets as a basis set for density functional pseudopotential calculations2008In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, p. 14109-Article in journal (Refereed)
  • 10.
    Glaz, Waldemar
    et al.
    Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań.
    Bancewicz, Tadeusz
    Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University.
    Godet, Jean Luc
    Laboratoire de Photonique D'Angers, Université D'Angers.
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Haskopoulos, Anastasios
    Department of Chemistry, University of Patras.
    Maroulis, George
    Department of Chemistry, University of Patras.
    Effects of anisotropic interaction-induced properties of hydrogen-rare gas compounds on rototranslational Raman scattering spectra: Comprehensive theoretical and numerical analysis2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 3, article id 34303Article in journal (Refereed)
    Abstract [en]

    A comprehensive study is presented of many aspects of the depolarized anisotropic collision induced (CI) component of light scattered by weakly bound compounds composed of a dihydrogen molecule and a rare gas (Rg) atom, H2-Rg. The work continues a series of earlier projects marking the revival of interest in linear light scattering following the development of new highly advanced tools of quantum chemistry and other theoretical, computational, and experimental means of spectral analyses. Sophisticated ab initio computing procedures are applied in order to obtain the anisotropic polarizability component's dependence on the H2-Rg geometry. These data are then used to evaluate the CI spectral lines for all types of Rg atoms ranging from He to Xe (Rn excluded). Evolution of the properties of CI spectra with growing polarizability/masses of the complexes studied is observed. Special attention is given to the heaviest, Kr and Xe based, scatterers. The influence of specific factors shaping the spectral lines (e.g., bound and metastable contribution, potential anisotropy) is discussed. Also the share of pressure broadened allowed rotational transitions in the overall spectral profile is taken into account and the extent to which it is separable from the pure CI contribution is discussed. We finish with a brief comparison between the obtained results and available experimental data

  • 11.
    Gustafsson, Magnus
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Classical calculations of radiative association in absence of electronic transitions2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 7, article id 74308Article in journal (Refereed)
    Abstract [en]

    A formula for the cross section of radiative association where no electronic transitions take place is derived and tested for diatomic molecules. The approach is based on classical mechanics and therefore it is valid for direct, i.e., non-resonant, radiative association. For the formation of carbon monoxide (CO) and the cyano radical (CN), in the X 1Σ+ and A 1Π states, respectively, the treatment reproduces the baselines of the cross sections obtained using quantum mechanical perturbation theory. The method overestimates the formation cross section of potassium sodide (NaK) by about 8%. For the lower mass diatoms hydrogen fluoride (HF) and deuterium hydride (HD), the formula overestimates the cross sections by 12% and 60%, respectively. The formula can be used alone for estimates of radiative association rate constants, or in combination with Breit-Wigner theory to include resonance contributions.

  • 12.
    Gustafsson, Magnus
    et al.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Antipov, Sergey V.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Franz, Jan
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Refined theoretical study of radiative association: cross sections and rate constants for the formation of SiN2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 137, no 10, article id 104301Article in journal (Refereed)
    Abstract [en]

    Radiative association of silicon mononitride (SiN) in its two lowest molecular electronic states is studied through quantum and classical dynamics. Special attention is paid to the behavior of the cross section at high collision energies. A modified expression for the semiclassical cross section is presented which excludes transitions to continuum states. This gives improved agreement with quantum mechanical perturbation theory at high energies. The high energy cross section is overestimated if conventional semiclassical theory is used. The modified semiclassical theory should be valid in general for radiative association transitions from an upper to a lower electronic state. We also implement a quantum dynamical optical potential method with the same type of modification. The rate coefficient is calculated using Breit–Wigner theory and the modified semiclassical formula for the resonance and direct contributions, respectively, for temperatures from 10 K to 20 000 K. A rapid decrease in the rate constant for formation of ground state SiN is observed above 2000 K which was not seen previously.

  • 13.
    Gustafsson, Magnus
    et al.
    University of Texas, Physics Department.
    Frommhold, Lothar
    University of Texas, Physics Department.
    The HD–He complex: Interaction-induced dipole surface and infrared absorption spectra2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 115, no 12, p. 5427-5432Article in journal (Refereed)
    Abstract [en]

    The collision-induced dipole surface of an HD molecule interacting with an He atom is derived from the ab initio dipole data of the H2–He complex [Gustafsson et al., J. Chem. Phys. 113, 3641, (2000)]. Collision-induced absorption spectra of gaseous mixtures of deuterium hydride and helium in the rotational and fundamental bands of HD are calculated, for comparison with an existing measurement taken at a temperature of 77 K. To that end, we integrate the close-coupled, radial Schrödinger equations, accounting for the anisotropy of the HD–He interaction potential. The computed absorption spectra generally agree reasonably well with the observed spectral profiles and intensities of the collision-induced spectra. We also consider the interference phenomena of the HD permanent dipole with the interaction-induced, supramolecular dipole by computing the wings of various R(j) lines and of the P1(1) line in single, binary collision limit. For comparison, the line broadening and shift for the P and R line shape parameters are also computed using the impact approximation. The close-coupled treatment of our calculation of the spectral profiles accounts for rotational level mixing in a nonperturbative manner. The treatment is fully quantum-mechanical and takes into account single binary collisions of HD and He.

  • 14.
    Gustafsson, Magnus
    et al.
    University of Texas, Physics Department.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Bailly, Denise
    Labaratoire de Photophysique Moléculaire, CNRS, Campus d’Orsay, France.
    Bouanich, Jean-Pierre
    Labaratoire de Photophysique Moléculaire, CNRS, Campus d’Orsay, France.
    Brodbeck, Claude
    Labaratoire de Photophysique Moléculaire, CNRS, Campus d’Orsay, France.
    Collision-induced absorption in the rototranslational band of dense hydrogen gas2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 119, no 23, p. 12264-12270Article in journal (Refereed)
    Abstract [en]

    Measurements of the H2–H2 collision-induced absorption spectra at temperatures of 297.5 and 77.5 K are reported in the frequency range from 1900 to 2260 cm−1 at gas densities ranging from 51 to 610 amagat. Ab initio calculations of the absorption are carried out for comparison with the measurements. In these calculations, for the lower temperature close-coupled equations describe the H2–H2scattering in the presence of a weak electromagnetic radiation field; the anisotropy of the H2–H2interaction is accounted for. For the room temperature calculations, the isotropic potential approximation is employed. Agreement of measured and calculated spectral shapes is observed. However, in the far wing, at large frequencies (≳2000 cm−1), discrepancies of measured and calculated spectral intensities are observed which are somewhat larger than the combined, estimated uncertainties of theory and measurement. These differences remain unexplained at this stage.

  • 15.
    Gustafsson, Magnus
    et al.
    Department of Chemistry, University of Gothenburg.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Li, Xiaoping
    Department of Chemistry, Michigan State University.
    Hunt, Katherine L.C.
    Department of Chemistry, Michigan State University.
    Roto-translational Raman spectra of pairs of hydrogen molecules from first principles2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 16, article id 164314Article in journal (Refereed)
    Abstract [en]

    We calculate the collision-induced, roto-translational, polarized, and depolarized Raman spectra of pairs of H2 molecules. The Schrödinger equation of H2–H2scattering in the presence of a weak radiation field is integrated in the close-coupled scheme. This permits the accounting for the anisotropy of the intermolecular potential energy surface and thereby it includes mixing of polarizability components. The static polarizability invariants, trace and anisotropy, of two interactingH2 molecules were obtained elsewhere [Li et al., J. Chem. Phys.126, 214302 (2007)] from first principles. Here we report the associated spherical tensor components which, along with the potential surface, are input in the calculation of the supramolecular Raman spectra. Special attention is paid to the interferences in the wings of the rotational S0(0) and S0(1) lines of the H2 molecule. The calculated Raman pair spectra show reasonable consistency with existing measurements of the polarized and depolarized Raman spectra of pairs of H2 molecules.

  • 16.
    Gustafsson, Magnus
    et al.
    University of Texas, Physics Department.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Meyer, Wilfried
    Fachbereich Chemie, Universität Kaiserslautern, Germany.
    Infrared absorption spectra by H2–He collisional complexes: The effect of the anisotropy of the interaction potential2000In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 113, no 9, p. 3641-3650Article in journal (Refereed)
    Abstract [en]

    As an extension of previous work which was based on the isotropic interaction approximation, absorption spectra in the rotational and fundamental bands of H2, induced by collisions with He, are calculated by numerical integration of the close-coupled Schrödinger equation to account for the anisotropy of the interaction potential. A refined quantum chemical dipole surface of interactingH2–He pairs is also obtained with an extended grid of molecular geometries. This dipole surface agrees generally well with previous results, but is smaller by about 5% in the isotropic overlap term which is significant only in the fundamental band. The effects of the anisotropy of the interaction are to reduce the peak intensities of the Q and S lines by roughly 10% and to increase absorption in the far wings by a similar amount. The accuracy of the dipole surface as well as that of the ab initiointeraction potential that enters the calculations of the spectra are believed to permit the prediction of absolute spectral intensities with an accuracy of about ±5%. Comparisons with the available measurements show very good agreement of the shapes of the spectral profiles, but the absolute intensities differ by up to 10% in some cases. These remaining differences between theory and measurements appear to be random and are generally smaller than the differences among comparable measurements. Our results should therefore provide a reliable basis for predicting absorption by H2–He pairs for temperatures and frequencies for which no laboratory measurements exist. This fact is of a special interest, for example, for the spectroscopic analyses of the atmospheres of the outer planets.

  • 17.
    Gustafsson, Magnus
    et al.
    University of Texas, Physics Department.
    Frommhold, Lothar
    University of Texas, Physics Department.
    Meyer, Wilfried
    Fachbereich Chemie, Universität Kaiserslautern, Germany.
    The H2–H complex: Interaction-induced dipole surface and infrared absorption spectra2003In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 118, no 4, p. 1667-1472Article in journal (Refereed)
    Abstract [en]

    A quantum chemical dipole surface of interacting H2–H pairs is obtained and collision-induced absorption spectra are computed for temperatures from 200 to 1000 K and frequencies from 0 to 6000 cm−1. The effect of the anisotropy of the potential energy is investigated and turns out to be almost negligible at the temperature for which a close-coupled quantum calculation was done. The smallness of the effect stems from the short range character of the anisotropic potential components for H2–H. Accordingly the isotropic potential approximation could be applied in most of the present calculations. The accuracy of the dipole surface as well as that of the ab initiopotential energy surface that enters the calculations of the spectra are believed to permit prediction of absolute spectral intensities with an accuracy in the 5% range.

  • 18.
    Gustafsson, Magnus
    et al.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Monge-Palacios, Manuel
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    The rate constant for radiative association of HF: Comparing quantum and classical dynamics2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 18, article id 184301Article in journal (Refereed)
    Abstract [en]

    Radiative association for the formation of hydrogen fluoride through the A1Π → X1Σ+ and X 1Σ+ → X1Σ+ transitions is studied using quantum and classical dynamics. The total thermal rate constant is obtained for temperatures from 10 K to 20 000 K. Agreement between semiclassical and quantum approaches is observed for the A 1Π → X1Σ+ rate constant above 2000 K. The agreement is explained by the fact that the corresponding cross section is free of resonances for this system. At temperatures below 2000 K we improve the agreement by implementing a simplified semiclassical expression for the rate constant, which includes a quantum corrected pair distribution. The rate coefficient for the X1Σ+ → X 1Σ+ transition is calculated using Breit-Wigner theory and a classical formula for the resonance and direct contributions, respectively. In comparison with quantum calculations the classical formula appears to overestimate the direct contribution to the rate constant by about 12% for this transition. Below about 450 K the resonance contribution is larger than the direct, and above that temperature the opposite holds. The biggest contribution from resonances is at the lowest temperature in the study, 10 K, where it is more than four times larger than the direct. Below 1800 K the radiative association rate constant due to X1Σ+ → X1Σ+ transitions dominates over A 1Π→ X1Σ+, while above that temperature the situation is the opposite.

  • 19.
    Gustafsson, Magnus
    et al.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Skodje, Rex T.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    The state-to-state-to-state model for direct chemical reactions: Application to D+H2 → HD+H2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, no 14, article id 144311Article in journal (Refereed)
    Abstract [en]

    A simple theoretical model is developed to predict the state-to-state dynamics of direct chemical reactions. Motivated by traditional ideas from transition state theory, expressions are derived for the reactive S matrix that may be computed using the local transition state dynamics. The key approximation involves the use of quantum bottleneck states to represent the near separable dynamics taking place near the transition state. Explicit expressions for the S matrix are obtained using a Franck-Condon treatment for the inelastic coupling between internal states of the collision complex. It is demonstrated that the energetic thresholds for various initial reagent states of the D+H2reaction can be understood in terms of our theory. Specifically, the helicity of the reagent states are found to correlate directly to the symmetry of the quantum bottleneck states, which thus possess very different thresholds. Furthermore, the rotational product state distributions for D+H2 are found to be associated with interfering pathways through the quantum bottleneck states.

  • 20.
    Gustafsson, Magnus
    et al.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Skodje, Rex T.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Zhang, Jianyang
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Dai, Dongxu
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Harich, Steven A.
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Wang, Xiuyan
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Yang, Xueming
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Erratum: Observing the stereodynamics of chemical reactions using randomly oriented molecular beams ( Journal of Chemical Physics (2006) 124 (241105))2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 125, no 22, article id 229901Article in journal (Refereed)
    Abstract [en]

    A new method is demonstrated to study the stereodynamics of simple chemical reactions that does not require the use of oriented (or aligned) molecular beams or measurements of the orientation state of product molecules. Instead, it is shown that by numerically combining accurate measurements of the state-to-state differential cross section for two or more rotational states of the reagent molecule, the separate contribution from the individual helicity states can be extracted. New molecular beam experiments are conducted for the D+H2→HD+Hreaction that confirm the validity of the method.

  • 21.
    Gustafsson, Magnus
    et al.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Skodje, Rex T.
    Department of Chemistry and Biochemistry, University of Colorado, Boulder.
    Zhang, Jianyang
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Dai, Dongxu
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Harich, Steven A.
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Wang, Xiuyan
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Yang, Xueming
    State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, People’s Republic of China.
    Observing the stereodynamics of chemical reactions using randomly oriented molecular beams2006In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 124, article id 241105Article in journal (Refereed)
    Abstract [en]

    A new method is demonstrated to study the stereodynamics of simple chemical reactions that does not require the use of oriented (or aligned) molecular beams or measurements of the orientation state of product molecules. Instead, it is shown that by numerically combining accurate measurements of the state-to-state differential cross section for two or more rotational states of the reagent molecule, the separate contribution from the individual helicity states can be extracted. New molecular beam experiments are conducted for the D+H2→HD+Hreaction that confirm the validity of the method.

  • 22.
    Głaz, Waldemar
    et al.
    Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University.
    Bancewicz, Tadeusz
    Nonlinear Optics Division, Faculty of Physics, Adam Mickiewicz University.
    Godet, Jean Luc
    Laboratoire de Photonique D'Angers, Université D'Angers.
    Gustafsson, Magnus
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Maroulis, George
    Department of Chemistry, University of Patras.
    Haskopoulos, Anastasios
    Department of Chemistry, University of Patras.
    Intermolecular polarizabilities in H2-rare-gas mixtures (H2-He, Ne, Ar, Kr, Xe): Insight from collisional isotropic spectral properties2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 141, no 7, article id 74315Article in journal (Refereed)
    Abstract [en]

    The report presents results of theoretical and numerical analysis of the electrical properties related to the isotropic part of the polarizability induced by interactions within compounds built up of a hydrogen H2 molecule and a set of noble gas atoms, Rg, ranging from the least massive helium up to the heaviest xenon perturber. The Cartesian components of the collisional polarizabilities of the H2-Rg systems are found by means of the quantum chemistry methods and their dependence on the intermolecular distance is determined. On the basis of these data, the spherical, symmetry adapted components of the trace polarizability are derived in order to provide data sets that are convenient for evaluating collisional spectral profiles of the isotropic polarized part of light scattered by the H2-Rg mixtures. Three independent methods of numerical computing of the spectral intensities are applied at room temperature (295 K). The properties of the roto-translational profiles obtained are discussed in order to determine the role played by contributions corresponding to each of the symmetry adapted parts of the trace polarizability. By spreading the analysis over the collection of the H 2-Rg systems, evolution of the spectral properties with the growing masses of the supermolecular compounds can be observed

  • 23.
    Hochberg, David
    et al.
    Centro de Astrobiología, Consejo Superior de Investigaciones Científicas, Instituto Nacional de T́cnica Aeroespacial (CSIC-INTA).
    Zorzano, María Paz
    Centro de Astrobiología, Consejo Superior de Investigaciones Científicas, Instituto Nacional de T́cnica Aeroespacial (CSIC-INTA).
    Morán, Federico
    Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense de Madrid.
    Spatiotemporal patterns driven by autocatalytic internal reaction noise2005In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 122, no 21, article id 214701Article in journal (Refereed)
    Abstract [en]

    The influence that intrinsic local-density fluctuations can have on solutions of mean-field reaction-diffusion models is investigated numerically by means of the spatial patterns arising from two species that react and diffuse in the presence of strong internal reaction noise. The dynamics of the Gray-Scott (GS) model [P. Gray and S. K. Scott, Chem. Eng. Sci. 38, 29 (1983); P. Gray and S. K. Scott, Chem. Eng. Sci.39, 1087 (1984); P. Gray and S. K. Scott,J. Phys. Chem. 89, 22 (1985)] with a constant external source is first cast in terms of a continuum field theory representing the corresponding master equation. We then derive a Langevin description of the field theory and use these stochastic differential equations in our simulations. The nature of the multiplicative noise is specified exactly without recourse to assumptions and turns out to be of the same order as the reaction itself, and thus cannot be treated as a small perturbation. Many of the complex patterns obtained in the absence of noise for the GS model are completely obliterated by these strong internal fluctuations, but we find novel spatial patterns induced by this reaction noise in the regions of parameter space that otherwise correspond to homogeneous solutions when fluctuations are not included

  • 24. Hoffmann, F.M.
    et al.
    Paul, Jan
    A FT-IRAS study of the vibrational properties of CO adsorbed on Cu/Ru(001): I. The structural and electronic properties of Cu1987In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 86, no 5, p. 2990-2996Article in journal (Refereed)
  • 25. Hoffmann, F.M.
    et al.
    Paul, Jan
    A FT-IRAS study of the vibrational properties of CO adsorbed on Cu/Ru(001): II: The dispersion of copper1987In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 87, no 3, p. 1857-1865Article in journal (Refereed)
    Abstract [en]

    The dispersion of copper adsorbed on a Ru(001) substrate has been investigated by using Fourier transform-infrared reflection absorption spectroscopy (FT-IRAS) and carbon monoxide as a molecular probe. Copper films evaporated at 85 K show a drastically different CO adsorption behavior compared to annealed films and exhibit a variety of adsorption sites. Characteristic C-O stretching frequencies allow us to identify small copper clusters of 1-4 atoms (2138-2123 cm-1), two-dimensional (2120-2110 cm-1) and three-dimensional (2098 cm-1) copper aggregates. After annealing to 250 K copper films at sub- and monolayer coverages form well-ordered small two- and three-dimensional copper aggregates. Formation of the epitaxial monolayer or islands of copper (2082 cm-1) requires a surprizingly mild annealing temperature of 350 K. Further annealing to 540 K results in increasing domain size of the copper islands or annealing of defect sites of the epitaxial monolayer. Multilayer coverages of copper evaporated at 85 K exhibit C-O stretching frequencies found for high-index copper single crystal surfaces, e.g., (211) and (755). This indicates a large number of surface steps and protruding copper atoms associated with rough films. Annealing to 540 K results in a smooth copper layer with preferential (111) orientation (2075 cm-1). The vibrational data presented here for Cu-Ru(001) agree well with previous reports of CO adsorption on copper single crystals, supported or evaporated films, and matrix-isolated clusters. They further allow us to determine the dispersion of supported Cu-Pt and Cu-Ni catalysts from data in the literature.

  • 26. Larsson, Andreas
    et al.
    Greer, James C.
    National Microelectronics Research Centre (NMRC), University College, Lee Maltings, Prospect Row, Cork.
    Harneit, Wolfgang
    Hahn-Meitner Institute, Glienicker Str. 100, D-14109 Berlin.
    Weidinger, Alois
    Hahn-Meitner Institute, Glienicker Str. 100, D-14109 Berlin.
    Phosphorous trapped within buckminsterfullerene2002In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 116, no 18, p. 7849-7854Article in journal (Refereed)
    Abstract [en]

    The chemical, spin, and thermodynamic properties of endohedral phosphorous were studied. A model for the interaction between the trapped group V atom and the fullerene cage was also discussed. It was observed that the repulsion between the group V atom's valence shell and the fullerene cage result in an exothermic binding of the atom within the cage.

  • 27. Larsson, Andreas
    et al.
    Tong, Longyu
    NMRC, University College, Lee Maltings, Cork.
    Cheng, Tongwei
    NMRC, University College, Lee Maltings, Cork.
    Nolan, Michael
    NMRC, University College, Lee Maltings, Cork.
    Greer, James C.
    NMRC, University College, Lee Maltings, Cork.
    Basis set study for the calculation of electronic excitations using Monte Carlo configuration interaction2001In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 114, no 1, p. 15-22Article in journal (Refereed)
    Abstract [en]

    A recipe for the calculation of excited states was presented, which constituted a significant step forward in making accurate excited state calculations. An acceptable energy difference between experimental and calculated energies to be less than 100 meV were also defined. The importance of a balanced description of the excited states and the ground state was emphasized and the resulting electronic transitions were compared with experimental values.

  • 28.
    Li, Yunguo
    et al.
    Applied Material Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH).
    Ahuja, Rajeev B.
    Applied Material Physics, Department of Materials and Engineering, Royal Institute of Technology (KTH).
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Communication: Origin of the difference between carbon nanotube armchair and zigzag ends2014In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 9, article id 91102Article in journal (Refereed)
    Abstract [en]

    In this work, we have found that the difference between armchair and zigzag ends of carbon nanotubes (CNTs) does not pertain at close study for individual bonds and thus alternative strategies need to be developed to reach the ultimate goals in selective growth. Based on first-principles simulations, the difference between binding strengths for CNTs of different chirality was investigated using hydrogen dissociation energies at their passivated ends. When all H atoms are removed collectively we find the well-known difference: that armchair bonds are much weaker than zigzag ones, which is typically seen for both CNT ends and graphene edges. However, when individual H atoms are removed we find almost no difference in hydrogen dissociation energies, small difference in bond lengths, which by association means small difference in C-C and M-C binding energies. We show convincingly that the difference in binding energy between armchair and zigzag ends is due to a fragment stabilization effect that is only manifested when all (or several neighbouring) bonds are broken. This is because at armchair ends/edges neighbouring dangling bonds can pair-up to form C≡C triple bonds that constitute a considerable stabilization effect compared to the isolated dangling bonds at zigzag ends/edges. Consequently, in many processes, e.g., catalytic growth where bonds are normally created/broken sequentially, not collectively, the difference between armchair and zigzag ends/edges cannot be used to discriminate growth of one type over the other to achieve chiral selective growth. Strategies are discussed to realize chirality selective growth in the light of the results presented, including addition of C2-fragments to favor armchair tubes

  • 29. Paul, Jan
    et al.
    Hoffmann, F.M.
    Alkali promoted CO bond weakening on aluminum: a comparison with transition metal surfaces1987In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 86, no 9, p. 5188-5195Article in journal (Refereed)
    Abstract [en]

    Data on the adsorption and decomposition of carbon monoxide on alkali promoted Al(100) are presented. CO dissociates on the potassium or sodium promoted surface and aluminum oxide and aluminum carbide form after annealing to 700 K. At intermediate temperatures EELS show alkali-CO complexes with vibrational frequencies ranging from 1060 to 2060 cm-1. A band at 1750 cm-1 was assigned to CO molecules coordinated to bulk potassium. CO vibrational spectra as well as work function measurements reveal an altered alkali dispersion as a function of preannealing temperature. Comparisons are made between the surfaces of aluminum and transition metals with respect to (i) alkali adsorption, (ii) hybridization between metal d states and CO π orbitals, (iii) the magnitude of unscreened (long-range) perturbations, and finally (iv) the energetics of carbide and oxide formation. Potassium but not sodium atoms bind strongly to aluminum carbide (Td>700 K). We suggest that potassium is rare among alkali metals not in its ability to promote CO dissociation but in preventing a downshift of the C 2pz orbital and thus carbide to graphite transformation.

  • 30.
    Pilkington, Georgia A.
    et al.
    Surface and Corrosion Science, Department of Chemistry, KTH Royal Institute of Technology.
    Harris, Kathryn
    System and Component Design, Department of Machine Design, KTH Royal Institute of Technology.
    Bergendal, Erik
    Surface and Corrosion Science, Department of Chemistry, KTH Royal Institute of Technology.
    Reddy, Akepati Bhaskar
    System and Component Design, Department of Machine Design, KTH Royal Institute of Technology.
    Pålsson, Gunnar K.
    Department of Physics and Astronomy, Division of Materials Physics, Uppsala University.
    Vorobiev, Alexei
    Department of Physics and Astronomy, Division of Materials Physics, Uppsala University.
    Antzutkin, Oleg N.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Glavatskih, Sergei
    System and Component Design, Department of Machine Design, KTH Royal Institute of Technology.
    Rutland, Mark W.
    Surface and Corrosion Science, Department of Chemistry, KTH Royal Institute of Technology.
    Electro-responsivity of ionic liquid boundary layers in a polar solvent revealed by neutron reflectance2018In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 148, article id 193806Article in journal (Refereed)
    Abstract [en]

    Using neutron reflectivity, the electro-responsive structuring of the non-halogenated ionic liquid (IL) trihexyl(tetradecyl)phosphonium-bis(mandelato)borate, [P6,6,6,14][BMB], has been studied at a gold electrode surface in a polar solvent. For a 20% w/w IL mixture, contrast matched to the gold surface, distinct Kiessig fringes were observed for all potentials studied, indicative of a boundary layer of different composition to that of the bulk IL-solvent mixture. With applied potential, the amplitudes of the fringes from the gold-boundary layer interface varied systematically. These changes are attributable to the differing ratios of cations and anions in the boundary layer, leading to a greater or diminished contrast with the gold electrode, depending on the individual ion scattering length densities. Such electro-responsive changes were also evident in the reflectivities measured for the pure IL and a less concentrated (5% w/w) IL-solvent mixture at the same applied potentials, but gave rise to less pronounced changes. These measurements, therefore, demonstrate the enhanced sensitivity achieved by contrast matching the bulk solution and that the structure of the IL boundary layers formed in mixtures is strongly influenced by the bulk concentration. Together these results represent an important step in characterising IL boundary layers in IL-solvent mixtures and provide clear evidence of electro-responsive structuring of IL ions in their solutions with applied potential.

  • 31.
    Shen, G.
    et al.
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Lu, X.
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology.
    A hybrid perturbed-chain SAFT density functional theory for representing fluid behavior in nanopores2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 22, p. 224706-Article in journal (Refereed)
    Abstract [en]

    A hybrid statistical mechanical model, which is fully consistent with the bulk perturbed-chain statistical associating fluid theory (PC-SAFT) in describing properties of fluids, was developed by coupling density functional theory with PC-SAFT for the description of the inhomogeneous behavior of real chain molecules in nanopores. In the developed model, the modified fundamental measure theory was used for the hard sphere contribution; the dispersion free energy functional was represented with weighted density approximation by averaging the density in the range of interaction, and the chain free energy functional from interfacial statistical associating fluid theory was used to account for the chain connectivity. Molecular simulation results of the density profile were compared with model prediction, and the considerable agreement reveals the reliability of the proposed model in representing the confined behaviors of chain molecules in an attractive slit. The developed model was further used to represent the adsorptions of methane and carbon dioxide on activated carbons, in which methane and carbon dioxide were modeled as chain molecules with the parameters taken from the bulk PC-SAFT, while the parameters of solid surface were obtained from the fitting of gas adsorption isotherms measured experimentally. The results show that the model can reliably reproduce the confined behaviors of physically existing substances in nanopores.

  • 32.
    Shen, Gulou
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lu, Xiaohua
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing University of Technology.
    A hybrid perturbed-chain SAFT density functional theory for representing fluid behavior in nanopores: Mixtures2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 139, no 19, article id 194705Article in journal (Refereed)
    Abstract [en]

    The perturbed-chain statistical associating fluid theory (PC-SAFT) density functional theory developed in our previous work was extended to the description of inhomogeneous confined behavior in nanopores for mixtures. In the developed model, the modified fundamental measure theory and the weighted density approximation were used to represent the hard-sphere and dispersion free energy functionals, respectively, and the chain free energy functional from interfacial statistical associating fluid theory was used to account for the chain connectivity. The developed model was verified by comparing the model prediction with molecular simulation results, and the agreement reveals the reliability of the proposed model in representing the confined behaviors of chain mixtures in nanopores. The developed model was further used to predict the adsorption of methane-carbon dioxide mixtures on activated carbons, in which the parameters of methane and carbon dioxide were taken from the bulk PC-SAFT and those for solid surface were determined from the fitting to the pure-gas adsorption isotherms measured experimentally. The comparison of the model prediction with the available experimental data of mixed-gas adsorption isotherms shows that the model can reliably reproduce the confined behaviors of physically existing mixtures in nanopores

  • 33.
    Szabo, Peter
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    A surface-hopping method for semiclassical calculations of cross sectionsfor radiative association with electronic transitions2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, article id 094308Article in journal (Refereed)
    Abstract [en]

    A semiclassical method based on surface-hopping techniques is developed to model the dynamics of radiative association with electronic transitions. It can be proven that this method is an extension of the established semiclassical formula used in the characterization of diatomic molecule-formation. Our method is tested for diatomic molecules. It gives the same cross sections as the former semiclassical formula but, contrary to the former method, it allows us to follow the fate of the trajectories after the emission of a photon. This means that we can characterize the rovibrational states of the stabilized molecules. Using semiclassical quantization, we can obtain quantum state-resolved cross sections or emission spectra for the radiative association process. The calculated semiclassical state-resolved spectra show general agreement with the result of quantum mechanical perturbation theory. Furthermore, our surface-hopping model is not only applicable for the description of radiative association but it can be used for semiclassical characterization of any molecular process where spontaneous emission occurs

  • 34.
    Verkhoturov, Stanislav V.
    et al.
    Department of Chemistry, Texas A&M University.
    Czerwinski, Bartlomiej
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Verkhoturov, Dmitriy S.
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Geng, Sheng
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Delcorte, Arnaud
    nstitute of Condensed Matter and Nanosciences - Bio and Soft Matter (IMCN/BSMA), Universit ́ e Catholique de Louvain, 1 Croix du Sud, B-1348 Louvain-la-Neuve, Belgium.
    Schweikert, Emile A.
    Department of Chemistry, Texas A&M University, College Station, Texas 77843-3144, USA.
    Ejection-ionization of molecules from free standing graphene2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 8, article id 084308Article in journal (Refereed)
    Abstract [en]

    We present the first data on emission of C60stimulated by single impacts of 50 keV C602+on the self-assembled molecular layer of C60deposited on free standing 2 layer graphene. The yield,Y, of C60emitted in the transmission direction is 1.7%. To characterize the ejection and ionization of molecules,we have measured the emission of C60from the surface of bulk C60(Y= 3.7%) and from a singlelayer of C60deposited on bulk pyrolytic graphite (Y= 3.3%). To gain insight into the mechanism(s) ofejection, molecular dynamic simulations were performed. The scenario of the energy deposition andejection of molecules is different for the case of graphene due to the confined volume of projectile-analyte interaction. In the case of 50 keV C602+impacts on graphene plus C60, the C atoms of theprojectile collide with those of the target. The knocked-on atoms take on a part of the kinetic energyof the projectile atoms. Another part of the kinetic energy is deposited into the rim around the impactsite. The ejection of molecules from the rim is a result of collective movement of the molecules andgraphene membrane, where the membrane movement provides the impulse for ejection. The efficientemission of the intact molecular ions implies an effective ionization probability of intact C60. Theproposed mechanism of ionization involves the tunneling of electrons from the vibrationally exitedarea around the hole to the ejecta

  • 35.
    Verkhoturov, Stanislav V.
    et al.
    Department of Chemistry, Texas AandM University, College Station.
    Geng, Sheng
    Department of Chemistry, Texas AandM University, College Station.
    Czerwinski, Bartlomiej
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Young, Amanda E.
    Materials Characterization Facility, Texas AandM University.
    Delcorte, Arnaud
    Universite Catholique de Louvain, Institute of Condensed Matter and Nanosciences - Bio and Soft Matter, Louvain-la-Neuve.
    Schweikert, Emile A.
    Department of Chemistry, Texas AandM University, College Station.
    Single impacts of keV fullerene ions on free standing graphene: Emission of ions and electrons from confined volume2015In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 143, no 16, article id 164302Article in journal (Refereed)
    Abstract [en]

    We present the first data from individual C60 impacting one to four layer graphene at 25 and 50 keV. Negative secondary ions and electrons emitted in transmission were recorded separately from each impact. The yields for Cn - clusters are above 10% for n ≤ 4, they oscillate with electron affinities and decrease exponentially with n. The result can be explained with the aid of MD simulation as a post-collision process where sufficient vibrational energy is accumulated around the rim of the impact hole for sputtering of carbon clusters. The ionization probability can be estimated by comparing experimental yields of Cn - with those of Cn 0 from MD simulation, where it increases exponentially with n. The ionization probability can be approximated with ejecta from a thermally excited (3700 K) rim damped by cluster fragmentation and electron detachment. The experimental electron probability distributions are Poisson-like. On average, three electrons of thermal energies are emitted per impact. The thermal excitation model invoked for Cn - emission can also explain the emission of electrons. The interaction of C60 with graphene is fundamentally different from impacts on 3D targets. A key characteristic is the high degree of ionization of the ejecta

  • 36.
    Wang, Y.L.
    et al.
    Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology.
    Sarman, Sten
    Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology.
    Kloo, Lars
    Applied Physical Chemistry, Department of Chemistry, KTH Royal Institute of Technology.
    Antzutkin, Oleg
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Glavatskih, Sergei
    System and Component Design, Department of Machine Design, KTH Royal Institute of Technology.
    Laaksonen, Aatto
    Department of Materials and Environmental Chemistry, Arrhenius Laboratory, Stockholm University.
    Solvation structures of water in trihexyltetradecylphosphonium-orthoborate ionic liquids2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 145, no 6, article id 064507Article in journal (Refereed)
    Abstract [en]

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

  • 37.
    Öström, Jonatan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Bezrukov, Dmitry S.
    Department of Chemistry, M. V. Lomonosov Moscow State University.
    Nyman, Gunnar
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Reaction rate constant for radiative association of CF+2016In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 144, no 4, article id 44302Article in journal (Refereed)
    Abstract [en]

    Reaction rate constants and cross sections are computed for the radiative association of carbon cations (C+) and fluorine atoms (F) in their ground states. We consider reactions through the electronic transition 11Π → X1Σ+ and rovibrational transitions on the X1Σ+ and a3Π potentials. Semiclassical and classical methods are used for the direct contribution and Breit–Wigner theory for the resonance contribution. Quantum mechanical perturbation theory is used for comparison. A modified formulation of the classical method applicable to permanent dipoles of unequally charged reactants is implemented. The total rate constant is fitted to the Arrhenius–Kooij formula in five temperature intervals with a relative difference of <3%. The fit parameters will be added to the online database KIDA. For a temperature of 10–250 K, the rate constant is about 10−21 cm3 s−1, rising toward 10−16 cm3 s−1 for a temperature of 30 000 K.

1 - 37 of 37
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