Isotope Effects In Exchange, Desorption, And Decomposition Of Water Molecules On Ru(0001) At Cryogenic Temperatures

Interactions of H2O and D2O with Ru(0001) were investigated in terms of isotope effects based on experiments of time-of-flight secondary ion mass spectrometry (TOF-SIMS) and reflection high-energy electron diffraction (RHEED). Tightly bound water molecules and/or hydroxyls in direct contact with the substrate remain up to 220 K after desorption of physisorbed water molecules at ca. 170 K. The template effect of the substrate during nucleation of the latter is hampered when the former are present at the interface, thereby aborting epitaxial growth of ice on the Ru(0001) surface. The tightly bound species is exchangeable with gas-phase water molecules at 190 K via the proton-transfer reaction, where no apparent isotope effects are recognizable. The isotope effect is observed during thermal desorption and decomposition processes of the tightly bound species at temperatures higher than 220 K: OD is more stable than OH in terms of recombinative desorption and further fragmentation into atomic species.