title: Coexistence of ice clusters and liquid-like water clusters on the Ru(0001) surface.
abstract: The RAIRS spectra of water adsorbed on Ru(0001) at 85 K are recorded from 600 cm-1to 4000 cm-1. 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-1) 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-1, 3210 ± 5 cm-1, 3300 ± 15 cm-1, 3430 ± 5 cm-1and 3570 ± 10 cm-1, 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.
authors.affiliation: Industrial Focus Group XUV Optics, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands. F.Liu-2@utwente.nl.
authors.forename: Feng
authors.identifier: http://orcid.org/0000-0001-5156-3098
authors.initials: F
authors.lastname: Liu
authors.affiliation: Industrial Focus Group XUV Optics, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands. F.Liu-2@utwente.nl.
authors.forename: J M
authors.initials: JM
authors.lastname: Sturm
authors.affiliation: Industrial Focus Group XUV Optics, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands. F.Liu-2@utwente.nl.
authors.forename: Chris J
authors.identifier: http://orcid.org/0000-0001-7020-2036
authors.initials: CJ
authors.lastname: Lee
authors.affiliation: Industrial Focus Group XUV Optics, MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands. F.Liu-2@utwente.nl.
authors.forename: Fred
authors.initials: F
authors.lastname: Bijkerk