XPS studies of alkali halogen oxides, ozone exposure to alkali halides and halate-halide reactions in thin-film water

Over the past ten years there have been several reports from laboratory experiments that have suggested that surface reactions at salt solution interfaces are an important component of the heterogeneous processing of sea salt. In this thesis we will approach this chemistry from a surface spectroscopy perspective by monitoring the changes in the composition of salt surfaces using X-ray photoelectron spectroscopy (XPS).;Chapter 1 is essentially a chapter of control experiments, whereby reference XPS spectra of commercially available alkali halogen oxides were taken. This was done, for the most part, because of the lack of XPS data on these types of materials. In Chapter 2, the heterogeneous reaction of ozone (O3) with dry alkali halide salts was investigated. The spectra acquired in Chapter 1 provided a reference by which to monitor whether the alkali halide salt surfaces oxidized upon exposure to ozone. At low O3 exposures the surface of KI reacted to form essentially a layer of KIO3 on the surface, with an estimated initial reactive uptake 5 x 10-4. NaCl and NaBr were essentially unreactive towards O3 at low O 3 exposures. At high O3 exposures there was an apparent nitrogen oxide contamination from the O3 source that ended up forming a layer of nitrate on the surfaces of the salts, and thereby (although it was very interesting) complicating the O3 uptake chemistry.;In Chapter 3, the knowledge gained from Chapters 1 and 2 was pulled together to study the reactions of halates with halides in thin films of water on salt surfaces. It was found that in these thin films, halate-halide reactions occurred in the absence of added acidity, which is in contrast to known kinetics in bulk aqueous solution. The rate of halide destruction followed zero order kinetics, which also does not occur in bulk solution. It is suggested that unique reactions occurred at the air-water interface of these thin films. Halate chemistry is largely unexplored in ambient sea-salt particles, and in light of these results, may be worth exploring as a potentially significant source of molecular halogens in the troposphere.