Interaction of ammonia molecules with the MgO(100) surface: Application to the measure of the effective ionic surface charge

Sidoumou, M.; Panella, V.; Suzanne, J.

doi:10.1063/1.468387

Cited by 29 publications

(18 citation statements)

References 20 publications

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“…The R factor is 0.2 which is larger than that for the distance 2.49 Å corresponding to the effective charge 61.2. Our tensor LEED analysis shows definitively a convergence towards 2.5 Å, consistent with the value 61.2 of the surface effective charge as proposed in previous experiments of NH 3 adsorbed on the same MgO(100) substrate [9]. Finally, we have tried to put the molecules above oxygen ions with the same orientational parameters and molecule-surface distance given by the calculations.…”

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confidence: 80%

“…Molecular adsorbates bearing strong dipole or quadrupole moments have been investigated on this surface. They are good probes of the surface electric field and have been used to evaluate the effective ionic charge q ‫ء‬ q͞e of the surface ions [9]. This effective charge is about 61.2, in agreement with theoretical models [10].…”

mentioning

confidence: 82%

“…In the present work, two different values of the effective ionic charge of the surface ions have been taken: 61.2 and 62. The latter value, q ‫ء‬ 62, corresponds to a totally ionic MgO crystal, whereas the former value, 61.2, has been determined, as mentioned above, from experiments [9] and theoretical calculations [10]. No temperature effects are introduced in the model.…”

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confidence: 99%

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Structure of Physisorbed Molecules on an Oxide Surface from Potential Calculations and Dynamical Low-Energy Electron Diffraction Analysis: Acetylene on MgO(100)

et al. 1997

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Semiempirical potential calculations have been combined with a dynamical low-energy electron diffraction analysis to determine the complete structure of molecules physisorbed on an oxide surface, namely, acetylene (C 2 H 2 ) adsorbed on MgO(100) at T 88 K. This allows determination of the adsorption sites and the molecule-molecule and molecule-substrate distances. The results are consistent with molecules that lie almost parallel to the surface in a herringbone structure. Neither molecule nor substrate exhibits significant distortions, due to the weak physisorption. [S0031-9007 (97)03254-7] PACS numbers: 68.55.Jk, 34.20.Gj, 61.14.Hg Molecular adsorption, including physisorption, on oxides is of special importance for catalysis, since oxides play major roles both as active catalysts and as supports for metallic catalyst particles [1]: Zeolites, in particular, have attracted much attention [2]. While strong metal-support interactions remain under extensive study [3], there is a need for studying surfaces that are accessible to a wider range of surface science techniques, primarily external single-crystal surfaces [4]. MgO provides a most favorable model oxide crystal for this purpose: It is itself used as a support in catalysis. It is furthermore used as support for the growth of high-T c superconductors. MgO provides high-quality single-crystal surfaces while it is also available as uniform powder on whose large surface area molecular adsorption can be studied with neutron diffraction. Calculations [5], as well as low-energy electron diffraction (LEED) dynamical analyses [6,7] and medium-energy ion scattering analysis [8], have shown that the bare MgO(100) surface is only slightly perturbed from its bulk structure. Molecular adsorbates bearing strong dipole or quadrupole moments have been investigated on this surface. They are good probes of the surface electric field and have been used to evaluate the effective ionic charge q ‫ء‬ q͞e of the surface ions [9]. This effective charge is about 61.2, in agreement with theoretical models [10]. Acetylene has a strong quadrupole moment which is expected to interact strongly with the surface electric field gradient and give a molecular arrangement with strong quadrupole-quadrupole interactions. LEED adsorption isotherms on MgO(100) surfaces [11] as well as volumetric isotherms on powders [12] have provided adsorbate-substrate and adsorbateadsorbate interaction energies which have been compared to semiempirical potential calculations [11]. However, the detailed equilibrium structure given by the theoretical model must still be confronted with experimental results. The dynamical analysis of LEED intensities provides a unique way to obtain the complete structure: molecular adsorption sites, molecule-substrate distance, and orientation, in addition to any relaxation within the molecules and the substrate. However, this analysis require an approximate knowledge of the monolayer structure to start with, since it is a perturbationlike method. This is the reason why our approach c...

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confidence: 82%

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confidence: 99%

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Structure of Physisorbed Molecules on an Oxide Surface from Potential Calculations and Dynamical Low-Energy Electron Diffraction Analysis: Acetylene on MgO(100)

et al. 1997

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“…The saturation coverage in UHV depends on temperature, but an absolute coverage measurement 8 shows that saturation occurs at 0.2 ML at 120 K. Volumetric measurements of the adsorption isotherm for ammonia on MgO powder estimate the isosteric heat of adsorption to be 17Ϯ3 kcal/mol in the low coverage limit. 9 Both the LITD measurements on single crystals and the volumetric measurements on powders show that the adsorption energy decreases as coverage increases, indicating a repulsive interaction between coadsorbed ammonia molecules. Electron diffraction 9 shows no long range order of adsorbed ammonia at submonolayer coverages though neutron diffraction 10 studies find short range ordering.…”

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confidence: 98%

“…9 Both the LITD measurements on single crystals and the volumetric measurements on powders show that the adsorption energy decreases as coverage increases, indicating a repulsive interaction between coadsorbed ammonia molecules. Electron diffraction 9 shows no long range order of adsorbed ammonia at submonolayer coverages though neutron diffraction 10 studies find short range ordering. Attempts to measure surface diffusion rates with LITD were not successful; diffusion over the length scales probed occurs so slowly that desorption competes with diffusion.…”

Section: Introductionmentioning

confidence: 98%

Ammonia adsorption on MgO(100): A density functional theory study

Nakajima

Doren

1996

The Journal of Chemical Physics

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Density functional theory study of some structural and energetic properties of small lithium clustersThe properties of ammonia adsorbed at flat, step and kink sites on a MgO͑100͒ surface have been investigated using density functional theory. A finite MgO cluster is used to represent the MgO͑100͒ surface. Bonding is primarily determined by electrostatic interactions, which can have long range effects on these ionic surfaces. To account for such effects, cluster models of various sizes have been compared and the effects of surrounding the cluster by an array of fixed point charges have been explored. Several different structures have been found for ammonia bound at the various surface sites. The calculated adsorption energy on a flat surface is 19-21 kcal/mol, which is in reasonable agreement with experimental estimates of 13-17 kcal/mol at low coverage. Binding at kink sites is strongly favored over binding on the flat surface and dissociation is feasible only at kink sites. The electrostatic environment has a much greater effect on adsorption at step and kink sites than on the flat surface. The reaction path for diffusion of ammonia on a flat MgO͑100͒ surface is explored. The nature of the ammonia-MgO interactions, the effects of the electrostatic environment, and considerations in the choice of cluster models are discussed.

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3.6.1.10 References for 3.6.1.

Suzanne¹

Adsorbed Layers on Surfaces

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Interaction of ammonia molecules with the MgO(100) surface: Application to the measure of the effective ionic surface charge

Abstract: Articles you may be interested inApplication of ion scattering spectroscopy to measurement of surface potential of MgO thin film under ion irradiation Appl. Phys. Lett. 92, 084104 (2008);

Cited by 29 publications

References 20 publications

Structure of Physisorbed Molecules on an Oxide Surface from Potential Calculations and Dynamical Low-Energy Electron Diffraction Analysis: Acetylene on MgO(100)

Structure of Physisorbed Molecules on an Oxide Surface from Potential Calculations and Dynamical Low-Energy Electron Diffraction Analysis: Acetylene on MgO(100)

Ammonia adsorption on MgO(100): A density functional theory study

3.6.1.10 References for 3.6.1.

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