9712381 Dibble This project uses laser-induced fluorescence (LIF) and quantum chemical calculations to determine rate coefficients for the isomerization and dissociation reactions of alkoxy radicals. These unimolecular reactions are poorly characterized, yet alkoxy radicals commonly dissociate or isomerize rather than reacting with molecular oxygen in the atmosphere. The competition among these three reactions has important implications for ozone formation throughout the troposphere. Data obtained in this study will help improve our understanding of alkoxy radical chemistry, and aid in the study of many other crucial atmospheric reactions involving alkoxy radicals. LIF will be used to probe transient concentrations of alkoxy radicals. LIF in the near UV has demonstrated enormous utility for spectroscopic and kinetic studies of alkoxy radicals. It possesses the sensitivity and time resolution necessary to carry out direct determination of absolute rate coefficients for isomerization and dissociation reactions. In this study, the LIF spectra of alkoxy radicals possessing at least four carbon atoms will be determined. The technique can distinguish between isomers of the larger alkoxy radicals. For those alkoxy radicals which are not amenable to study by this experimental approach, quantum mechanical calculations will be employed to estimate the effects of structure on reaction rates for isomerization and dissociation. Benchmark studies on species for which experimental data is available will be used as a reference to estimate unimolecular reaction rates not yet established by experiment.