Reaction of water with clean surfaces of MnO(100)

Water adsorption on the MnO(100) single crystal surface was quantitatively monitored using chemical shifts in the O 1s core level spectra. We find tha t the initial reactions at low water vapor pressures of 10(-8)-10(-4) Torr are limited to a small fraction of a monolayer and involve dissociation of water at or near defect centers resulting in surface hydroxyls. Even at the se low pressures, there is an increase in water adsorption with increasing dosing time. Water uptake increases dramatically for vapor pressures betwee n 10(-4) and 10(-2) Torr and then stabilizes above 10(-2) Torr. At this pre ssure, hydroxyl coverages slightly exceed a monolayer. Hydroxyl species for med on this surface are unstable and can be removed by annealing to 200 deg rees C. These data are compared with those from similar studies of the inte raction of water vapor with MgO(100) and the surfaces of iron oxides (alpha -Fe2O3 and Fe3O4), and some quantitative similarities and differences are d iscussed. In particular, the role of cooperative interactions in the conden sed water overlayer in surface hydroxylation is emphasized.