Abstract

The interaction of water with the basal plane (0001) of α-Fe₂O₃ (hematite) is a fundamental and challenging topic in the fields of surface science and earth science. Despite intensive investigations, many issues remain unclear especially due to the lack of direct spectroscopic evidence. Here, water adsorption on the pristine Fe-terminated α-Fe₂O₃(0001) surface was investigated by polarization-dependent infrared reflection absorption spectroscopy and X-ray photoelectron spectroscopy in conjunction with calculations from density functional theory. The combined results provide solid evidence that the interaction of water with α-Fe₂O₃(0001) is dominated by the heterolytic dissociation yielding an O_wD species coordinated in atop-configuration to surface Fe³⁺ and an O_sD species resulting from the deuterium/hydrogen transfer to an adjacent substrate O^2–. Both isolated hydroxyl groups do not feature any hydrogen bonding, while the intact water molecules were identified as minor species that are bound to surface Fe³⁺ ions and interact via a relatively strong H-bonding with substrate oxygen. Water adsorption on α-Fe₂O₃(0001) at 230 and 200 K leads to the formation of water thin films including bilayers and multilayers, which are characterized by different types of intermolecular H-bonds.

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