Cavity ringdown spectroscopy of chlorine-​substituted peroxy radicals: Reaction kinetics with nitric oxide

Abstract

Peroxy radicals (RO_2) are ubiquitous intermediates in the oxidn. of volatile org. compds. Their competing fates govern subsequent free radical chem. in the troposphere. Reaction of RO_2 with nitric oxide (NO) has two product channels: assocn. to an org. nitrate (RONO_2) or oxidn./redn. to nitrogen dioxide (NO_2) and an alkoxy radical (RO). In this work, we present measurements of the RO_2 + NO rate const. at several pressures for peroxy radicals formed in the chlorine-initiated oxidn. of ethene, propene, 2-butene, and isoprene. We monitor the decay of peroxy radicals through their weak and structured A-X transition in the near-IR using cavity ringdown spectroscopy (CRDS) and the simultaneous kinetics and ringdown (SKaR) technique. Chlorine is a minor tropospheric oxidant found in marine regions and its substitution yields insight into the structure and reactivity of RO_2 species. We compare our results to prior work in the literature at a fixed pressure and to measurements on hydroxyl-substituted peroxy radicals.