A kinetic and spectroscopic study of chemistry relating to the atmospheric role of iodine species

Abstract

The impact of halogen chemistry on important atmospheric processes such as ozone depletion and (potentially) climate regulation is becoming increasingly apparent. Yet only the most fundamental atmospheric chemistry of halogen species is included in global tropospheric models. Spectroscopic measurements of the concentration of halogen species within the Earth's atmosphere, and the accurate determination of kinetic information regarding the rates and mechanisms of chemical processes in the laboratory, greatly facilitate the evolution of our quantitative understanding of the atmospheric role of halogen species, ultimately leading to their inclusion in atmospheric chemistry models. The research presented in this thesis addresses previously un-investigated areas (or areas requiring further elucidation) of iodine chemistry. Specifically, Chapter Three uses new spectroscopic data to reassess the viability of a laser-induced fluorescence (LIF) instrument for the detection of ambient iodine monoxide radicals (10), a key species in the atmospheric chemistry of iodine, which may help to enhance our understanding of important atmospheric processes via its spatially resolved detection. Chapter Four presents a kinetic and spectroscopic investigation into the mechanism and products of the reaction of CH21 radicals with 02, which has potential implications for particle formation in the marine boundary layer (MBL). The reaction of Cl atoms with alkyl iodides, CH3I and CH212, has been studied in detail by the detection of adducts formed in these reactions, which have been observed by LIF for the first time, and is the subject of Chapter Five. As part of the course of this PhD, the reaction kinetics of the reaction of 10 with dimethyl sulphide (DMS) was investigated. The results obtained have led to a re-evaluation of the atmospheric significance of this reaction. The data obtained assist the development of our knowledge of the atmospheric chem istry of iodine species and, at a more fundamental level, the electronic structure and physical processes of gas phase species