Adsorption and electrostatic drift of molecules on the surface of a KCl crystal

Abstract

The energy of adsorption of KCl molecules on (001)KCl is calculated approximately by taking into account the electrostatic polarization and the Born component. Energies are estimated for KCl molecules aligned parallel or normal to the face surface. The normal orientation is more advantageous by 0.318 eV than the parallel arrangement on an infinite face. Among the two antiparallel normal-to-surface configurations, the one in which the cation of the admolecule faces an anion on the lattice surface is more advantageous by 0.02 eV than the opposite configuration (anion of the admolecule facing cation on the surface). Electrostatic potentials on (001)KCl are calculated in the vicinity of a vertex, a kink or a step, and a point of intersection of a crystal edge and a step. Differences found in energies of adsorption of ions and molecules in different points of these regions show a possibility of oriented drift of molecules and ions to these singular points of the real surface. The lengths of oriented and random diffusion paths during the residence time of the molecule in the adsorbed state become comparable in the vicinity of these singular points. Commensurability must be expected in areas with radius ∼95a0 around a vertex, ∼160a0 around a step origin, and ∼190a0 around a kink (a0=3.14 A ̊ is the interionic distance in KCl). © 1981.