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 spectroscopy ~MIES!, ultraviolet photoelectron spectroscopy @UPS ~HeI!#, and by thermal programmed desorption ~TPD!. Methanol wets the MgO surface and adsorbs nondissociatively within the first monolayer with the hydroxyl group oriented 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 fraction of the preadsorbed methanol remains within the topmost surface layer during the buildup of the water multilayer. Temperature-dependent measurements show that the adsorption and desorption dynamics of both water and methanol are governed by intermolecular interactions rather than adsorbate–substrate interactions. © 1999 American Institute of Physics. @S0021-9606~99!70505-2#