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  • 1
    Electronic Resource
    Electronic Resource
    Structure and dynamics of ice Ih films upon HCl adsorption between 190 and 270 K. II. Molecular dynamics simulations (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 5150-5157 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical molecular dynamics simulations are carried out between 190 and 250 K on an ultrathin ice film doped by HCl deposition with a coverage varying from 0.3 to 1.0 monolayer. These conditions are similar to those defined in the experiments described in the companion paper. Within the assumption that the hydracid molecule remains in its molecular form, the order parameters and the diffusion coefficients for the H2O molecules are determined in the HCl doped ice film, and compared to the experimental data. The residence times of HCl at the ice surface are also calculated. Below 200 K, the HCl molecules are found to remain localized at the ice surface, while above 200 K, the HCl diffusion inside the film is easy and leads to a strong disorder of the ice structure. Although the formation of hydrates cannot be interpreted by the present calculations, the lowering of the ice melting temperature by 15 K measured in neutron experiments for an HCl doped ice film is qualitatively explained by simulation results. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1454991
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  • 2
    Electronic Resource
    Electronic Resource
    The passage of small molecules through a water film supported by MgO(100): Transfer times from molecular dynamics simulations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 1184-1193 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The passage of small pollutant molecules (HCl, CO2) through a thin water film supported on a MgO substrate at 300 K has been studied by constrained classical molecular dynamics simulations. The calculated free energy profile of the pollutants exhibits two minima, one at the gas/liquid film interface, and the other inside the film near the ionic substrate. Lifetimes of the pollutants in these two sites have been characterized by unconstrained simulations. The residence times in these sites are in the range of a few tens of picoseconds. The transfer times from one site to the other, and the times spent by the pollutants in the liquid and at the liquid/gas interface (∼ one hundred ps) are always twice longer for CO2 than for HCl. This difference is interpreted in terms of correlated dynamics of HCl and H2O due to hydrogen bond interactions with water. The duration of the hydrogen bond Cl–H⋅⋅⋅O increases significantly (∼2 ps) at the film surface with respect to its value inside the film (〈1 ps). © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481897
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  • 3
    Electronic Resource
    Electronic Resource
    Adsorption of acetone molecules on proton ordered ice. A molecular dynamics study (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9898-9908 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption of acetone molecules on a proton ordered ice Ih(0001) surface was studied using classical molecular dynamics simulations between 50 and 150 K. At low coverage, we show that acetone molecules form an ordered monolayer on this ice surface, which is stable for T≤100 K. At higher temperature, it exhibits orientational disordering, though local translational order remains. Preliminary simulations at higher coverage indicates the formation of additional ordered layers above the first monolayer, which are also stable below 100 K. These results support previous conclusions on the acetone/ice interactions based on the interpretation of experimental data. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481627
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamics of ice layers deposited on MgO(001): Quasielastic neutron scattering experiments and molecular dynamics simulations (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 6371-6381 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamical behavior of a thin film of ice Ih deposited on MgO(001) surface has been investigated both experimentally and theoretically. Incoherent neutron quasielastic scattering experiments, using uniform MgO powders, show that a quasiliquid water layer of monolayer thickness exists at T=265 K. The translational mobility of this layer, with a diffusion coefficient Dt=1.5×10−5 cm2 s−1, is close to that of liquid water. At T=270 K, the thickness of the quasiliquid layer increases to about two layers, showing no appreciable change in the Dt value but an increase of the rotational mobility from 6×109 s−1 to 1.2×1010 s−1. Classical molecular dynamics simulations are performed to determine the translational and orientational order parameters and diffusion coefficients of the supported ice film as a function of temperature within 190 and 270 K, and to compare the results with those obtained for bulk ice. It is shown that the whole supported ice film is much more disordered than bulk ice, with melting temperature around 235 K for the TIP4P potential used, while the melting temperatures of the outermost layer are nearly the same (around 220 K) for the supported film and bulk ice. Comparison of the values of the translational and orientational diffusion coefficients obtained in simulation and experiments displays a good agreement. Although the calculated value of the surface melting temperature is underestimated by 15% with respect to the experimental result, the present study indicates clearly the influence of the support on the melting process. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355238
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  • 5
    Electronic Resource
    Electronic Resource
    Adsorption of polar molecules on substrates with strong electric surface fields: from aggregates to monolayers
    Amsterdam : Elsevier
    Chemical Physics Letters 209 (1993), S. 340-346 
    Details
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0009-2614(93)80027-M
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  • 6
    Electronic Resource
    Electronic Resource
    Interpretation of the polarization infrared spectrum of CO2 monolayers adsorbed on ionic substrates (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7229-7237 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We interpret the polarization infrared spectrum of linear molecules adsorbed on ionic substrates on the basis of semi-classical interaction potentials. The frequency shifts and splittings and the intensities of the infrared signals are analyzed in terms of strong electrostatic surface fields with the additional influence of the lateral coupling between admolecules. Application to the CO2 monolayer adsorbed on clean NaCl and MgO(100) surfaces is discussed. A consistent quantitative comparison between calculated and measured peak intensities of the polarization spectrum requires the presence of two types of domains for the layer, oriented along the perpendicular step directions 〈100〉 and 〈010〉 with a relative weight 1:4. This corroborates the experimental assignment of the parallel and perpendicular polarized peaks associated with the bending and asymmetric stretching vibrational modes of the admolecule. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469034
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  • 7
    Electronic Resource
    Electronic Resource
    A molecular dynamics study of the structure of water layers adsorbed on MgO(100) (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 3245-3254 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations are performed at various temperatures (150-300 K) and coverages (1-3 layers) on the adsorption of water on a clean MgO(100) surface using semiempirical potentials. At the monolayer coverage, a number of very stable (m×n) structures are obtained which differ only by the mutual orientations of the molecules. The p(3×2) phase observed above 180 K in low-energy electron diffraction (LEED) and helium atom scattering (HAS) experiments is shown to be the most stable at 200 K and above this temperature. It contains six inequivalently oriented molecules which lie flat above the cation sites with the hydrogens pointing approximately along the Mg rows. When the water coverage increases, a layer of icelike hexagonal structure within which the water molecules are hydrogen bonded is formed above the stable monolayer. This overlayer, which is stable at 150 K, is not hydrogen bonded to the stable monolayer. At 300 K it tends to break up and to aggregate into a 3D ice structure with strong hydrogen bonding. Examination of the calculated oxygen-oxygen distances dOO in the monolayer and in the icelike overlayer, and the comparison with the correlation diagram of the frequency shift and bandwidth of the water infrared spectrum versus dOO give a very consistent interpretation of the observed polarized infrared signals. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476915
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  • 8
    Electronic Resource
    Electronic Resource
    Adsorption of ortho and para H2 on NaCl(001) (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6435-6449 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fourier transform infrared spectroscopy (FTIR) experiments together with interaction potential calculations are performed to interpret the adsorption–desorption properties of para and ortho H2 molecules physisorbed on the (001) faces of NaCl crystallites. Isotherms of the adsorption process show preferential adsorption of para-H2 from gaseous normal-H2 at surface temperature around 10 K. Isobars of the desorption process show preferential desorption of para-H2 from a mixed ortho-H2 and para-H2 adsorbate. A quantum description of the molecular motions corroborates preferential adsorption of p- and (M=±1) o-H2 on the cation sites, as proposed in previous classical studies. It is shown that the adsorption energy is smaller for the para than for the (M=±1) ortho species in agreement with experimental measurement of desorption energy, while (M=0) o-H2 is only slightly bound to the substrate. This indicates that the ionic surface can discriminate all the H2 species. The determination of the bar spectrum for a set of independently adsorbed H2 species can interpret most of the infrared signals assigned to adsorption on the terrace sites. More specially the experimental behavior, with temperature and coverage, of the frequencies and relative intensities of the pure vibrational peaks and of the translation–vibration combination bands is very well explained in terms of hindered external motions of the admolecule. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477288
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  • 9
    Electronic Resource
    Electronic Resource
    Structure of CO monolayer adsorbed on NaCl(100) from molecular dynamics (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8453-8462 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical molecular dynamics calculations are performed between 25 and 55 K to investigate the structure and the dynamics of the CO monolayer adsorbed on NaCl(100) surface. The simulation is based on the most recent potential available for this system and the results are compared with experimental data issued from polarization infrared spectroscopy and helium atom scattering. We show that the monolayer adopts a (2×1) structure at 25 K, with two molecules per unit cell. The corresponding angular motions perpendicular and parallel to the surface are clearly librational. As temperature rises, the molecular axes remain tilted with a librational motion perpendicular to the surface, while the translational and orientational motions parallel to the surface behave much more freely, leading to an orientationally disordered structure at 55 K. These features suggest that dynamical effects in the (2×1) layer are responsible for an ordered/disordered transition observed as temperature increases, instead of the phase transition from ordered (2×1) to (1×1) structures which was previously inferred. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472699
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  • 10
    Electronic Resource
    Electronic Resource
    Experimental and theoretical studies of the monolayer structure of OCS adsorbed on NaCl(001): Coexistence of orientationally inequivalent phases (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 5271-5283 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of a physisorbed carbonyl sulfide (OCS) monolayer on a well-defined NaCl single crystal surface has been studied by helium atom scattering (HAS), low energy electron diffraction (LEED) and polarized Fourier-transform infrared spectroscopy, in the temperature range 30–100 K. The monolayer growth proceeds via large islands and both HAS and LEED indicate a (2×1) commensurate structure with two molecules per unit cell. The binding energy is estimated to be about 0.26 eV from desorption experiments. By contrast, the occurrence of three intense and three weaker absorption peaks in the infrared spectrum of the asymmetric stretching vibration ν3 is difficult to reconcile with the conclusions drawn from HAS and LEED. Therefore semi-empirical potential calculations are performed to determine the monolayer structure. Energy minimization rules out a high molecular density for the layer, and shows the existence of two isoenergetical (2×1) and (2×2) phases with respectively two and four molecules per unit cell, which differ only by the orientations of the molecules. Because of their similar geometry, these two structures cannot be discriminated by HAS and LEED, but the mixing of these two phases with different vibrational couplings between the admolecules provides a reasonable interpretation of the main features of the infrared spectrum. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473526
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