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-oxid ized W(100) surface have been examined over a wide temperature range ( 25-700 K) with thermal desorption spectroscopy (TDS), low energy ion s cattering (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 E SDIAD are used to monitor the surface chemistry of (H2O)-O-18 on the o xidized W(100) surface. ESD and ESDIAD data show no evidence for diffu sion 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 temperatur e 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 monola yer) dissociates upon adsorption at 25 K to form adsorbed (OH)-O-16 an d (OH)-O-18. NO stable OH species remains on the oxidized W(100) surfa ce above about 350 K.