A look at atmospheric chemistry through the back door: PEI spectroscopy of anionic precursors to transient species

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Many of the principal drivers of atmospheric chemistry are short-lived reactive small molecules known as "radicals," the characterization of which is challenging because it is difficult to prepare them in a laboratory in sufficient quantities to study them. In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Caroline Chick Jarrold uses a unique approach to preparing radicals by (1) stabilizing them with a negative charge, then (2) gleaning detailed information about the neutral radicals by using lasers to selectively detach the electrons in a way that the energy of the electrons precisely reflects the properties of the radicals. The specific molecules of interest are involved in production of ozone in the part of the atmosphere with negative impact on human health. Outreach is being done, in part, through her institution's STEM Summer Scholars Institute.This project combines low-temperature preparation of radical species and their anionic precursors with anion photoelectron imaging (PEI) spectroscopy. This combination of tools is being applied to OH-isoprene adducts, and species formed by ozonolysis of isoprene, which may include Criegee intermediates (carbonyl oxides believed to be formed during ozonolysis), along with non-covalent complexes the intermediates form with H2O and O2. The oxidation of isoprene (2-methyl-1,3-butadiene) by OH and O3 leads to the formation of a wide range of reactive open-shell molecules, the kinetics of which has been a very active area of research. The spectroscopic data from the proposed studies complements kinetics studies with more detailed electronic and molecular structural information. Additionally, the effects of water, which influences isomerization and reaction barrier heights, and O2, which can both photosensitize and react with the transients, are being probed. Spectroscopic analysis is supported collaboratively by quantum wavepacket ab initio molecular dynamics studies. The broader impacts of this project include an increase in current understanding of the complex, interconnected web of atmospheric processes, in addition to highly technical training for a postdoctoral research associate, graduate students, and undergraduates in the context of an area of global importance.