Interaction of methanol and water on MgO(100) studied by ultraviolet photoelectron and metastable impact electron spectroscopies

The coadsorption of methanol (CH3OH) and water (D2O) on the MgO(100)/Mo(100 ) surface at 100 K has been studied by metastable impact electron spectrosc opy (MIES), ultraviolet photoelectron spectroscopy [UPS (HeI)], and by ther mal programmed desorption (TPD). Methanol wets the MgO surface and adsorbs nondissociatively within the first monolayer with the hydroxyl group orient ed toward the substrate. In coadsorption experiments, methanol wets a water precovered MgO surface; however, adding water to a methanol precovered MgO surface does not yield a water-only surface. Essentially, a constant fract ion of the preadsorbed methanol remains within the topmost surface layer du ring the buildup of the water multilayer. Temperature-dependent measurement s show that the adsorption and desorption dynamics of both water and methan ol are governed by intermolecular interactions rather than adsorbate-substr ate interactions. (C) 1999 American Institute of Physics. [S0021-9606(99)70 505-2].