| 1. |
- Engdahl, Anders, et al.
(författare)
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Axial motion of water hydrogen halide and water halogen complexes in argon matrices
- 1986
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 84:4, s. 1981-1987
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Tidskriftsartikel (refereegranskat)abstract
- The infrared spectra of the water (H2O, HDO, D2O) complexes with HCl, HBr, HI Cl2, Br2, and I2 have been studied in argon matrices in the 11 to 25 K interval. In all cases, water acts as a lone-pair donor. The hydrogen halide complexes are effectively planar and rotate around the axis through the heavy atoms. For the water halogen complexes, the results are less clear, but a similar rotation, coupled to low wave number bending motions, seems possible.
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| 2. |
- Engdahl, Anders, et al.
(författare)
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On the relative stabilities of H- And D-bonded water dimers
- 1987
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 86:4, s. 1819-1823
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Tidskriftsartikel (refereegranskat)abstract
- The infrared spectra of water dimers formed from H2O, D 2O, and HDO in krypton matrices have been recorded. Thermal equilibria between H- and D-bonded dimers have been studied. D bonding is preferred, and H-bonded dimers are approximately 60 cm-1 less stable than D-bonded dimers. The energy difference seems to be due to the higher value of the intermolecular out-of-plane H-bond shear vibration compared to the corresponding D-bond vibration.
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| 3. |
- Forsman, Hans, et al.
(författare)
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Thermal conductivity at high pressure of solid odd-numbered n-alkanes ranging from C9H20 to C19H40
- 1984
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 80:6, s. 2804-2807
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity λ has been measured in the temperature range 190–330 K and at pressures up to 1.0 GPa for the various phases of odd‐numbered n‐alkanes ranging from C9H20 to C19H40. We used the transient hot‐wire technique. At 0.03 GPa, the thermal conductivity for the plastic crystal phase was about 0.2 W m−1 K−1 and showed no clear variation with chain length. For all n‐alkanes the increase in λ at the liquid → plastic crystal phase transition was about 35%. At low pressures λ increased monotonically with increasing chain length for the low temperature phase. At pressures above 0.5 GPa and at 273 K the λ results of C9H20 and C11H24 indicate that these two substances transform into another, more close‐packed, structure than that of the longer odd‐numbered n‐alkanes.
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| 4. |
- Herder, CE, et al.
(författare)
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Interactions of hydrocarbon monolayer surfaces across N-alkanes: A steric repulsion
- 1989
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Ingår i: Journal of Chemical Physics. - 0021-9606 .- 1089-7690. ; 90, s. 5801-5805
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Tidskriftsartikel (refereegranskat)abstract
- We present results of force measurements between hydrocarbon monolayer surfaces across n-alkanes (hexane, decane, and tetradecane). The interaction id qualitatively different from that of any previously system and, in particular, bears no resemblance to an oscillatory solvation force. Instead, the force is repulsive from about 2.5 nm, with the exeption of a shallow minimum just outside a force maximum at 0.8-0.9 nm. At smaller separations the force becomes attractive and there is a waek adhesion at contact. We suggest that the force law is due to a steric effect____a repulsive interaction originating in restrictions on chain conformations of the alkanes at small surface separations. This interaction is acessible via simple mean-field theories. The similarity of the liquid-liquid and liquid-surface interactions allows this to dominate over solvation effects. The results are of significance for interaggregate interactions in lamellar liquid crystals, microemulsions, and surfactant- stabilized dispersions.
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| 5. |
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| 6. |
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| 7. |
- Hoffmann, F.M., et al.
(författare)
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A FT-IRAS study of the vibrational properties of CO adsorbed on Cu/Ru(001) : II: The dispersion of copper
- 1987
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 87:3, s. 1857-1865
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
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| 9. |
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| 10. |
- Panas, Itai, 1959, et al.
(författare)
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The mechanism for the O2 dissociation on Ni(100)
- 1989
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 1089-7690 .- 0021-9606. ; 90, s. 6791-6801
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Tidskriftsartikel (refereegranskat)abstract
- The dissociation of O2 on Ni(100) has been studied using a cluster model approach. The three principally different reaction pathways, over an on‐top position, over a bridge position, and over a fourfold hollow position, were considered. The dissociation mechanisms were found to be very similar for these pathways. In the entrance channel a chemisorbed, peroxo‐form, of molecular O2 is first formed, which is strongly bound to the Ni(100) surface by two polar covalent bonds. The binding energy at the fourfold hollow site is found to be 78 kcal/mol, which is about 20 kcal/mol larger than for the other two sites, and much larger than the chemisorption energies for the experimentally observed O2 on Pt(111) and Ag(110). The reason for this difference is discussed. In a simplified valence‐bond picture the wave function of this molecularly bound O2 has a large component of a πu to πg excited state of O2. The dissociation of O2 then proceeds by two stepwise electron transfers from the surface over to the O2 3σu orbital, which completes the breaking of the O–O bond. In this latter process the energy passes over a local barrier, which is still far below the long distance asymptote, however. The local barrier height is much higher for the fourfold hollow dissociation, 35 kcal/mol over the local molecular minimum, than for the other two pathways, where the barrier height is only 6–8 kcal/mol. The 3d orbitals on nickel remain passive for all the three dissociation pathways, which is in line with the fact that also nontransition metals dissociate O2. This behavior is in contrast to the dissociation of H2 on Ni(100), where the 3d orbitals play a key role for the on‐top dissociation.
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| 11. |
- Paul, Jan, et al.
(författare)
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Alkali promoted CO bond weakening on aluminum : a comparison with transition metal surfaces
- 1987
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 86:9, s. 5188-5195
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 12. |
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