Reversibility of water dissociation on the MgO (100) surface

Using ab initio molecular dynamics, we have studied water adsorbed on the perfect MgO (100) surface. We show an important difference of the atomic structures of the water deposit calculated at 0 K and at finite temperatures. This suggests that use of the static results in order to analyze and interpret the experimental data can lead to false conclusions. We further find that water dissociated on the MgO surface may desorb in the molecular form. Until now the experimentally observed reversibility of the adsorption isotherms has been interpreted as a signature of molecular rather than dissociative adsorption. We show that this interpretation may be invalid.