RUI: Overall Rate Constant and Nitrate Branching Ratio Measurements for the Reactions of Alkene-Derived Peroxy Radicals with Nitric Oxide

Oberlin College, Oberlin OH

Investigators

Abstract

The tropospheric chemistry of ozone formation and destruction depends on many factors. One of the key gas-phase chemical reactions is the oxidation of nitric oxide by hydroperoxyl and organic peroxyl radicals. For hydroperoxyl and smaller organic peroxyl radicals, the reactions proceed almost exclusively by conversion of nitric oxide to nitrogen dioxide accompanied by formation of alkoxy radicals. The latter usually react with oxygen to form hydroperoxyl radicals. Larger and more complex, multiply substituted organic peroxyl radicals exhibit a second reaction pathway, leading to the formation of organic nitrates. The rate coefficients for this second reaction channel have been studied for some simple, straight-chained alkylperoxy radicals, but data are sparse and inconsistent for more complex radicals, such as those derived from the reaction of hydroxyl radicals with alkenes (double bond containing hydrocarbons). This study involves the systematic examination of the organic peroxyl radical plus nitric oxide reaction kinetics and branching ratios to form organic nitrates for radicals derived from a number of alkenes containing two to five carbon atoms. The peroxy radicals derived from hydroxyl radical-alkene reactions are called beta-hydroxy peroxy radicals, and have been studied relatively little. The technique of turbulent flow chemical ionization mass spectroscopy will be used to control the experimental conditions and quantify the yields of reaction products. Studies will be performed as a function of temperature. These data will be extremely useful for atmospheric chemical modeling, but can also be used to build structure-reactivity relationships that may allow prediction of yields from other, unmeasured species. This research will be carried out at an undergraduate institution with significant utilization of undergraduate research assistants in the project.