On the question of the stability of water layer on Ru(0001): electron-activated dissociation

There exist diverse and conflicting views on the stability of first molecular layer of water on the Ru(0001). Here we report the effect of electron irradiation on the rate of H$_{2}$O and D$_{2}$O dissociations when they adsorbed on ruthenium surface at low temperature (T$\le $100K). Our results show clearly that a molecular D$_{2}$O layer wets the surface and is thermally stable up to desorption. H$_{2}$O dissociates partly at elevated temperature to an extent which depends strongly on the exact heating procedures. Electron impact leads to partial dissociation of both H$_{2}$O and D$_{2}$O with extremely high cross section (e.g. $\sim $10$^{-15}$ cm$^{2}$ at 90 eV), and even electrons of very low energy (down to even 1 eV) are effective. We conclude that many reports on the system such as the LEED $I-V$ analysis of D$_{2}$O geometry by Held and Menzel and others have been influenced by the partial dissociation induced by slow electrons, and/or impurities in the layers. The results of DFT calculations concerning the stability of the adsorbed H$_{2}$O layer have to be viewed and interpreted with caution.