Coexistence of ice clusters and liquid-like water clusters on the Ru(0001) surface.

The RAIRS spectra of water adsorbed on Ru(0001) at 85 K are recorded from 600 cm to 4000 cm. Measured at water coverages from 0.13 ML to 2.0 ML, the RAIRS spectra suggest that chemisorption of water on Ru(0001) depends on coverage. Water adsorbs on a clean Ru surface as chemisorbed ice-like clusters (likely through an O-Ru bond) up to 0.33 ML. Above this coverage, the chemisorbed layer saturates. Upon more exposure, water adsorbs as a liquid-like H-bonded layer without bonding to the Ru substrate. The chemisorbed water absorbs 7 times less IR per molecule than the liquid-like structure, which indicates that the orientation of the chemisorbed water is more parallel to the surface. Additionally, the influence of water-Ru bonding on H-bonding is reflected in the OH symmetric stretching mode. Under perturbation from water-Ru bonding, a large red shift (40 cm) in the free OH stretching frequency is observed in the chemisorbed clusters. By deconvoluting the main H-bonded OH stretching peak into five Gaussian sub-bands at 2945 ± 5 cm, 3210 ± 5 cm, 3300 ± 15 cm, 3430 ± 5 cm and 3570 ± 10 cm, changes in the H-bonding network are rationalized in terms of H-bonding motifs. The donor-acceptor-acceptor motif is significant only in the chemisorbed clusters. On the other hand, the donor-acceptor motif dominates in the liquid-like structure, which increases the disorder present in the adlayer. Although chemisorption is suppressed above 0.33 ML, no structural changes in the ice-like clusters are observed up to multilayer coverage. Therefore, ice-like and liquid-like water coexist in a meta-stable state at 85 K.