Ab initio investigation of the thermochemistry, spectroscopy and dynamics of reactions between mercury and reactive halogen species
Recent measurements in the Arctic troposphere have revealed episodic depletions of mercury during polar sunrise. The depletion events are thought to be the result of reactions between gas phase elemental mercury with reactive halogen species. The goal of this work has been to characterize reactions between mercury and reactive halogen species with accurate ab initio calculations. The main body of the thesis is divided into eight chapters and two appendices with Chapter 1 being an introduction and summary. Chapter 2 discusses the calculation of potential energy curves for the ground and low-lying excited states of the BrC1 molecule. BrC1 is thought to be a major source of photolyzable halogens in the arctic troposphere. In Chapter 3 the characterization of the ground state of HgO is discussed. The accurate dissociation energy that was calculated rules out the involvement of HgO in the mercury depletion events. The recombination of Hg + Br atoms may be the first step in the mercury depletion events and Chapter 4 discusses ab initio calculations and quasiclassical trajectory calculations that were used to calculate the rate constant for this process. The thermochemistry of reactions between mercury and iodine containing species is covered in Chapter 5. It has been hypothesized that BrO plays a significant role in the mercury depletion events. The reaction of HgBr (HgC1) with BrO (CIO) can lead to the formation of mercury hypohalite species and calculations on these molecules are discussed in Chapter 6. Heterogeneous chemistry may play a role in mercury depletion events and the effect of aqueous microsolvation on a number of mercury-halogen reactions is investigated in Chapter 7. Cadmium should undergo similar reactions with halogen species, but little is known about gas phase reactions involving cadmium. Chapter 8 details accurate calculations on the thermochemistry of reactions between mercury and reactive halogen species. The appendices are manuscripts on which the dissertation's author was a contributor, but not the primary author. Appendix 1 details accurate characterization of the halogen oxide molecules CIO, BrO, IO and their anions. Appendix 2 describes calculations carried out on the rate of the HgBr + Br reaction.