Water dissociation on defective sites on the NaCl(100) surface. A quantum ab initio study

The dissociative adsorption of water on defective NaCl(100) surface is inve stigated by the embedded cluster method at the UHF/MP2 level of approximati on. The potential energy surfaces associated with OH bond breaking are calc ulated on step sites and on vacancies (V-s and F-s centers). The barriers o f activation on a step and on a V-s center are very high and cannot account for the dissociation of water on defective NaCl surfaces experimentally ob served at 240 K. On the contrary, the barrier of activation on F-s centers fulfills this condition. An optimal adsorption geometry is proposed where a ll the products of the reaction are trapped into the vacancy. This model is compared to the EEL and NEXAF spectroscopy results.