Surface Adsorption and Migration Energies for KCl

The binding and migration energies for a ${\mathrm{K}}^{+}$ ion on a (100) KCl surface are calculated. It is found that the most stable ${\mathrm{K}}^{+}$ site is about an interionic lattice spacing above a ${\mathrm{Cl}}^{-}$ surface ion and the binding energy is 0.68 ev. The activation energy for lateral diffusion is 0.23 ev and the estimated vibration frequencies are ${10}^{12}$ ${\sec }^{-1\mathrm{}}$ along the surface and 2.8×${10}^{12}$ ${\sec }^{-1\mathrm{}}$ normal to the surface. From these figures it is shown that the mean path length of the ion is about 2×${10}^{-4\mathrm{}}$ cm; the binding energy for an absorbed KCl molecule is found to be about 0.36 ev. This leads to the conclusion that the molecule will travel at most a few lattice spacings before evaporating. Some effects of this on crystal growth and additive coloring are discussed briefly.