title: Effects of chemical complexity on the autoxidation mechanisms of endocyclic alkene ozonolysis products: from methylcyclohexenes toward understanding α-pinene.
abstract: Formation of highly oxidized, multifunctional products in the ozonolysis of three endocyclic alkenes, 1- methylcyclohexene, 4-methylcyclohexene, and α-pinene, was investigated using a chemical ionization atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometer with a nitrate ion (NO3(-)) based ionization scheme. The experiments were performed in borosilicate glass flow tube reactors at room temperature (T = 293 ± 3 K) and at ambient pressure. An ensemble of oxidized monomer and dimer products was detected, with elemental compositions obtained from the high-resolution mass spectra. The monomer product distributions have O/C ratios from 0.8 to 1.6 and can be explained with an autocatalytic oxidation mechanism (=autoxidation) where the oxygen-centered peroxy radical (RO2) intermediates internally rearrange by intramolecular hydrogen shift reactions, enabling more oxygen molecules to attach to the carbon backbone. Dimer distributions are proposed to form by homogeneous peroxy radical recombination and cross combination reactions. These conclusions were supported by experiments where H atoms were exchanged to D atoms by addition of D2O to the carrier gas flow. Methylcyclohexenes were observed to autoxidize in accordance with our previous work on cyclohexene, whereas in α-pinene ozonolysis different mechanistic steps are needed to explain the products observed.
authors.affiliation: †Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.
authors.forename: Matti P
authors.initials: MP
authors.lastname: Rissanen
authors.affiliation: ‡Department of Chemistry, University of Helsinki, P.O. Box 55, 00014 Helsinki, Finland.
authors.forename: Theo
authors.initials: T
authors.lastname: Kurtén
authors.affiliation: †Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Sipilä
authors.affiliation: §Department of Atmospheric Sciences, University of Washington, Seattle, Washington 98195, United States.
authors.forename: Joel A
authors.initials: JA
authors.lastname: Thornton
authors.affiliation: †Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.
authors.forename: Oskari
authors.initials: O
authors.lastname: Kausiala
authors.affiliation: †Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.
authors.forename: Olga
authors.initials: O
authors.lastname: Garmash
authors.affiliation: ∥Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark.
authors.forename: Henrik G
authors.initials: HG
authors.lastname: Kjaergaard
authors.affiliation: †Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.
authors.forename: Tuukka
authors.initials: T
authors.lastname: Petäjä
authors.affiliation: †Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.|⊥Department of Applied Physics, University of Eastern Finland, 70211 Kuopio, Finland.|#Aerodyne Research Inc., 45 Manning Road, Billerica, Massachusetts 01821, United States.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Worsnop
authors.affiliation: †Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.
authors.forename: Mikael
authors.initials: M
authors.lastname: Ehn
authors.affiliation: †Department of Physics, University of Helsinki, P.O. Box 64, 00014 Helsinki, Finland.
authors.forename: Markku
authors.initials: M
authors.lastname: Kulmala