The adsorption and reaction of H2O on clean and oxygen covered Ag(110) |
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Authors: | EM Stuve RJ Madix BA Sexton |
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Institution: | Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA;Physical Chemistry Department, General Motors Research Laboratories, Warren, Michigan 48090, USA |
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Abstract: | The adsorption and reaction of water on clean and oxygen covered Ag(110) surfaces has been studied with high resolution electron energy loss (EELS), temperature programmed desorption (TPD), and X-ray photoelectron (XPS) spectroscopy. Non-dissociative adsorption of water was observed on both surfaces at 100 K. The vibrational spectra of these adsorbates at 100 K compared favorably to infrared absorption spectra of ice Ih. Both surfaces exhibited a desorption state at 170 K representative of multilayer H2O desorption. Desorption states due to hydrogen-bonded and non-hydrogen-bonded water molecules at 200 and 240 K, respectively, were observed from the surface predosed with oxygen. EEL spectra of the 240 K state showed features at 550 and 840 cm?1 which were assigned to restricted rotations of the adsorbed molecule. The reaction of adsorbed H2O with pre-adsorbed oxygen to produce adsorbed hydroxyl groups was observed by EELS in the temperature range 205 to 255 K. The adsorbed hydroxyl groups recombined at 320 K to yield both a TPD water peak at 320 K and adsorbed atomic oxygen. XPS results indicated that water reacted completely with adsorbed oxygen to form OH with no residual atomic oxygen. Solvation between hydrogen-bonded H2O molecules and hydroxyl groups is proposed to account for the results of this work and earlier work showing complete isotopic exchange between H216O(a) and 18O(a). |
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