Spectroscopy and Unimolecular Decay Dynamics of Reaction Intermediates in Atmospheric Chemistry

Abstract: Our research is focused on reaction intermediates that generate hydroxyl radicals (OH), often called the atmosphere’s detergent. The OH radical is one of the most powerful oxidizing agents in the troposphere, which reacts rapidly with other molecules, including most volatile organic compounds emitted in the atmosphere. Our studies have characterized transient carbonyl oxide intermediates, known as Criegee intermediates, in the chemical reaction pathways for alkene ozonolysis, an important non-photolytic source of OH radicals. Our studies have also revealed prototypical carbon-centered hydroperoxyalkyl radicals (•QOOH), critical intermediates in alkane oxidation of volatile organic compounds in the atmosphere and combustion of hydrocarbon fuels in low temperature (< 1000 K) environments, which regenerates OH radicals. Our experimental studies utilize IR action spectroscopy and time-resolved IR pump-UV probe measurements of OH products. Our experimental studies and complementary theory reveal the chemical reaction pathways under controlled laboratory conditions as well as their impact in realistic atmospheric and combustion chemistry.