Water Molecular Beam Scattering at alpha-Al2O3(0001): An Ab Initio Molecular Dynamics Study

作者：Heiden Sophia; Wirth Jonas; Campen R Kramer; Saalfrank Peter^*

来源：Journal of Physical Chemistry C, 2018, 122(27): 15494-15504.

DOI：10.1021/acs.jpcc.8b04179

Recent molecular beam experiments have shown that water may adsorb molecularly or dissociatively on an a Al2O3(0001) surface, with enhanced dissociation probability compared to "pinhole dosing", i.e., adsorption under thermal equilibrium conditions. However, precise information on the ongoing reactions and their relative probabilities is missing. In order to shed light on molecular beam scattering for this system, we perform ab initio molecular dynamics calculations to simulate water colliding with alpha-Al2O3(0001). We find that single water molecules hitting a cold, clean surface from the gas phase are either reflected, molecularly adsorbed, or dissociated (so-called 1-2 dissociation only). A certain minimum translational energy (above 0.1 eV) seems to be required to enforce dissociation, which may explain the higher dissociation probability in molecular beam experiments. When the surface is heated and/or when refined surface and beam models are applied (preadsorption with water or water fragments, clustering and internal preexcitation in the beam), additional channels open, among them physisorption, water clustering on the surface, and so-called 1-4 and 1-4' dissociation.

• 出版日期2018-7-12