XPS LINESHAPE ANALYSIS OF POTASSIUM COADSORBED WITH WATER ON NI(111)

The line profiles of XP spectra of H2O/K/Ni(111) were investigated for K submonolayer coverages. The K2p spectra exhibit a strong alteration of lineshape with increasing water coverage. Without coadsorbed water a significant asymmetry was found which decreased rapidly and indepen dently of the potassium precoverage with increasing water exposure up to THETA(H2O) = 0.7. The asymmetry observed in the K2p spectra is assi gned to a coupling of the potassium adatoms to the electronic structur e of the nickel substrate. The coadsorption of water suppresses this m echanism via a loosening of the potassium-nickel coupling. Since the d ecrease of asymmetry is independent of the potassium coverage, it is c oncluded that this process is due to an adsorbate-substrate interactio n between the water and the nickel substrate only. This contradicts mo dels in which the coadsorption of water and potassium on metal substra tes is manifested in hydration of the potassium adatoms.