Adsorption and reaction of water on oxidized tungsten: Thermal desorption and electron stimulated desorption measurements

The adsorption and decomposition of water, (H2O)-O-18, on an O-16-oxidized W(100) surface have been examined over a wide temperature range (25-700 K) with thermal desorption spectroscopy (TDS), low energy ion scattering (LEIS) and electron stimulated desorption (ESD), and ESD ion angular distribution (ESDIAD). TDS is used to determine the coverage and the range of desorption temperature of (H2O)-O-18, and to identify desorption products from the oxidized W(100) surface, while ESD and ESDIAD are used to monitor the surface chemistry of (H2O)-O-18 on the oxidized W(100) surface. ESD and ESDIAD data show no evidence for diffusion of (H2O)-O-18 on the oxidized W(100) surface between 25 K and 120 K. TDS demonstrates that the majority of water adsorbed in the first monolayer at 25 K remains molecular and desorbs with a peak temperature of similar to 155 K. However, both TDS and ESD measurements indicate that a very small percentage of (H2O)-O-18 (similar to 8% of a monolayer) dissociates upon adsorption at 25 K to form adsorbed (OH)-O-16 and (OH)-O-18. NO stable OH species remains on the oxidized W(100) surface above about 350 K.