Hydrophobic interactions between water and pre-adsorbed D on the stepped Pt(533) surface

Abstract

We have studied the interaction of Pt(533) with varying coverages of water and varying coverages of pre-adsorbed deuterium (D_ad) under ultra-high vacuum conditions. We use temperature-programmed desorption and reflective absorption infrared spectroscopy techniques to study the properties of these layers. Results show that deuterium’s preference to adsorb at step edges nulls the step-induced stabilization of water through an electronic effect. However, deuterium atoms at step edges do not block adsorption sites for water and water still wets the entire (111) terrace. With increasing deuterium coverage on terraces, formation of smaller, less-ordered water structures replaces formation of hexamer ring structures. Near deuterium saturation, water preferentially forms 3-dimensional amorphous solid water (ASW) clusters at the steps. The typical phase transition of ASW to crystalline ice is observed in these clusters. Although exchange of D_ad with H₂O occurs both at steps and terraces and is dependent on both surface coverages, the preference of water molecules to cluster at the step sites on the hydrophobic, deuterium-saturated Pt(533) surface biases exchange toward steps.