Structure and Energetics of the Water/NaCl(100) Interface

Abstract

A series of correlation-corrected periodic Hartree-Fock (PHF) calculations have been performed to evaluate the structure of a single layer of water adsorbed on NaCl(100). This work was motivated by differing experimental observations which assign the water/NaCl interface structure as either a monolayer, with a single adsorbate binding site, or a 4×2 bilayer model. Quantum mechanical binding energies were computed for several adsorbate/surface geometries corresponding to 1×1 and 2×1 monolayer structures and 4×2 bilayer structures. The calculations indicate that the binding energy per water molecule for the monolayer and bilayer models are very similar; the estimated PHF and correlation-corrected binding energies are 10 and 14 kcal/mol, respectively, for both models. When measured per unit surface area the 4×2 bilayer is energetically favored because it has a 50% greater packing density than the monolayer. The computed binding energies are consistent with experiment. These data show that the monolayer structure may be stable (or metastable) at low water coverages, but as the coverage is increased the bilayer structures become more favorable. The quantum mechanical data imply that the structure of the water/NaCl interface will be very sensitive to the sample preparation and experimental techniques used. The calculated binding energies for the 4×2 water bilayer geometries reveal the existence of many local minima on the potential energy surface which could result in the domaining of water on the NaCl(100) surface.

Atomic structure and energetics of adsorbed water on the NaCl(001) surface

“…While extensive investigations of water on the surfaces of metals, semiconductors and oxides have been carried out, 1-5 a determination of the structure of adsorbed water has been often controversial. Especially, the water/NaCl system [6][7][8][9][10][11][12][13][14][15][16][17][18] is of particular interest because of a crucial role in various areas such as environmental science and biophysics. The detailed knowledge of the adsorption structure of water on the NaCl surface would provide useful information related to the heterogeneous chemical reactions in the troposphere over oceans.…”

“…The detailed knowledge of the adsorption structure of water on the NaCl surface would provide useful information related to the heterogeneous chemical reactions in the troposphere over oceans. 19,20 Despite experimental 7,8 and theoretical [9][10][11][12][13][14][15] efforts to understand adsorbed water on the NaCl(001) surface, there is a controversy on the structure of the two-dimensional (2-D) phase which is formed before the condensation of threedimensional phases. Using low energy electron differaction (LEED) analysis together with ultraviolet photoelectron spectroscopy and x-ray photoelectron spectroscopy, Fölsch et al 7 suggested a puckered quasi-hexagonal bilayer structure of c͑4 ϫ 2͒ symmetry.…”

“…Classical simulations using model potentials have predicted either 1 ϫ 1 monolayer or c͑4 ϫ 2͒ bilayer structures depending on the calculational methods. A semiempirical calculation 11 and a periodic Hartree-Fock calculation 12 found that the 1 ϫ 1 structure is slightly more stable than the c͑4 ϫ 2͒ structure. The theoretical difficulty in determining water layer structure on NaCl(001) arises from the competing water-water and water-surface interactions, leading to several local minima on the potential energy surface whose energy differences are within a few meV.…”

Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

“…In addition to this technological importance, the nature of the interaction between ionic compounds and metals and ionic compounds and semiconductors raises fundamental questions [14]. Finally, it has been found that surface reactions involving atmospheric pollutants and NaCl crystallite may impact tropospheric ozone concentrations [16][17][18][19][20].…”

“…Currently, there is a renewed interest in this compound, since recent studies in the field of atmospheric chemistry have linked surface reactions between NaCl and common gaseous pollutants such as HN03, N205, N02 and C10N02 to the production of ozone reducing gas-phase Cl atoms [16][17][18][19][20].…”