Investigations on the influence of substrate geometry of flat and stepped ruthenium surfaces Ru(0001) and Ru(10(1)over-bar8) on the adsorption kinetics of H2O and D2O.

The desorption kinetics of H2O and D2O were studied on a flat Ru(0001) and a stepped Ru(<10(1)over bar8>) surface by TDS, Delta phi measurements (120 to 300 K) and LEED. In accordance with other authors we observed three typical desorption peaks for H2O on Ru(0001) (C, 155 K; A(2), 190 K; and A(1), 212 K), and the respective peaks for the isotope effect for D2O on Ru(0001), characterized by a missing A(1) peak. Isothermal Delta phi measurements were performed in order to determine the different desorption kinetics for H2O and D2O. Neither for D2O nor for H2O the desorption of the A(2) state can be described by first order kinetics. Especially for the A(2) peak of H2O, we observed an initial range of first order kinetics followed by a strong deviation, which could be described by Avrami kinetics or lateral interactions. Also, Delta phi measurements during desorption give evidence for a complicated adsorption kinetic process. In order to modify the water bilayer structure, a stepped Ru(<10(1)over bar8) surface was used for comparison. These measurements are in progress and should give further information about the isotope effect.