Metastable Impact Electron Spectroscopy (MIES) and Reflection Absorption Infrared Spectroscopy (RAIRS) Study of Acetic Acid Interacting with Amorphous Solid Water

The interaction of cyclic dimers of acetic acid with amorphous solid water (D 2 O) on polycrystalline silver was investigated. Metastable impact electron spectroscopy (MIES) was utilized to obtain information on the electronic structure of the outermost surface. Reflection absorption infrared spectroscopy (RAIRS) allowed for the identification of the acetic acid species and provided information on their hydration and the water-induced fragmentation. The interpretation of the results required also the study of the interaction of acetic acid with the neat silver substrate. On amorphous solid water (ASW), the acetic acid species quickly saturate the dangling OD groups present at the water surface at a coverage of less than 0.5 layers. In the first layer, the cyclic acid dimers break up under the influence of their interaction with the D 2 O molecules. For coverages >0.5 layers, strong lateral interaction between the acid molecules is responsible for the completion of the first adlayer. The second and following layers formed at 124 K consist of cyclic dimers. The splitting of the cyclic dimers by their interaction with the amorphous solid water, followed by their hydration, allows for a detailed characterization of the various acetic acid species resulting from the acetic acid−water interaction.