D Abstraction by H at a Ru(001) Surface Covered with D2O Molecules

The mechanism for the hydrogen abstraction (ABS) reaction at the D2O covered Ru(001) surface was investigated. HD desorption rates were measured at theta(D2O) <= 3 ML. The apparent reaction order of HD desorption was approximately 1.7, which is almost equal to the value of 1.6 +/- 0.1 measured on clean Ru(001) surfaces. The HD desorption rates were analyzed using the same equation previously proposed for the clean Ru surface, which consists of three rate terms due to the hot atom (HA), hot complex (HC) and Langmuir-Hinshelwood (LH) mechanisms. The surface area enclosed by the hexagonal ring structure of the first water layer is sufficiently large to assure complete energy relaxation of excess H atoms from the hot atom states at which HA-mediated ABS occurs to the supersaturation coverage of thermodynamically unstable adatoms, which results in ABS by the LH mechanism. (C) 2011 The Japan Society of Applied Physics