Interfacial Dushman-like Chemistry in Hydrated KIO3 Layers Grown on KI

Ozone is known to readily oxidize the heavier alkali halides in the form of sea salt aerosols, and this chemistry is thought to be a probable candidate for the formation of reactive gas-phase halogens in the troposphere. Water that becomes adsorbed at the interface following the oxidation process is believed to play a vital role in the mechanisms that release these gas-phase halogens. We have carried out studies that utilize X-ray photoemission spectroscopy and atomic force microscopy to follow the surface chemistry and topography of KIO 3 films as they are exposed to water vapor at room temperature. The KIO 3 films were grown under dry conditions by the heterogeneous reaction of ozone with a model low defect density KI(100) single crystal. As the water vapor pressure is increased above the surface dissolution point, the KIO 3 layer becomes solvated and ionic mobility at the surface increases. This mobility results in a ripening process that creates large crystallites of KIO 3 . The inhomogeneous KIO 3 layer continues to evolve at relative humidities near the bulk deliquescence point of the KI(100) substrate. Under these conditions, surface-adsorbed water molecules dissociate at defect sites generated during the initial heterogeneous reaction process and provide the necessary protons to initiate a Dushman-like surface reaction, where IO 3 − and I − react to release gas-phase iodide compounds. Vacancies created in lattice sites during the release of gas-phase iodide species are replaced by OH − groups to form a stable adlayer of KOH (which is likely partially hydrated). As a result of the KOH × H 2 O adlayer, which does not react further with O 3, only a portion of the particle’s iodide content is available for reaction.