Reversibility of water dissociation on the MgO (100) surface

Using nb initio molecular dynamics, we have studied water adsorbed on the p erfect MgO (100) surface. We show an important difference of the atomic str uctures 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 interp ret the experimental data can lead to false conclusions. We further find th at water dissociated on the MgO surface may desorb in the molecular form. U ntil now the experimentally observed reversibility of the adsorption isothe rms has been interpreted as a signature of molecular rather than dissociati ve adsorption. We show that this interpretation may be invalid.