title: Observation of the simplest Criegee intermediate CH2OO in the gas-phase ozonolysis of ethylene.
abstract: Ozonolysis is one of the dominant oxidation pathways for tropospheric alkenes. Although numerous studies have confirmed a 1,3-cycloaddition mechanism that generates a Criegee intermediate (CI) with form R1R2COO, no small CIs have ever been directly observed in the ozonolysis of alkenes because of their high reactivity. We present the first experimental detection of CH2OO in the gas-phase ozonolysis of ethylene, using Fourier transform microwave spectroscopy and a modified pulsed nozzle, which combines high reactant concentrations with rapid sampling and sensitive detection. Nine other product species of the O3 + C2H4 reaction were also detected, including formaldehyde, formic acid, dioxirane, and ethylene ozonide. The presence of all these species can be attributed to the unimolecular and bimolecular reactions of CH2OO, and their abundances are in qualitative agreement with published mechanisms and rate constants.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Caroline C
authors.initials: CC
authors.lastname: Womack
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA.
authors.forename: Marie-Aline
authors.initials: MA
authors.lastname: Martin-Drumel
authors.affiliation: Department of Science and Mathematics, Coker College, Hartsville, SC 29550, USA.
authors.forename: Gordon G
authors.initials: GG
authors.lastname: Brown
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Field
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA.
authors.forename: Michael C
authors.initials: MC
authors.lastname: McCarthy
keywords: Criegee intermediates; atmospheric chemistry; kinetics; microwave spectroscopy; ozonolysis; reaction dynamics; tropospheric chemistry