Synchrotron photoionization measurements of OH-initiated cyclohexene oxidation: ring-preserving products in OH + cyclohexene and hydroxycyclohexyl + O2 reactions.

Earlier synchrotron photoionization mass spectrometry experiments suggested a prominent ring-opening channel in the OH-initiated oxidation of cyclohexene, based on comparison of product photoionization spectra with calculated spectra of possible isomers. The present work reexamines the OH + cyclohexene reaction, measuring the isomeric products of OH-initiated oxidation of partially and fully deuterated cyclohexene. In particular, the diredly measured photoionization spectrum of 2-cyclohexen-1ol differs substantially from the previously calculated Franck Condon envelope, and the.oroduct spectrum can be fit with no contribution from ring-opening. Measurements of H2O2 photolysis in the presence of C6D10 establish that the 2,ddition elimination product incorporates the hydrogen atom from the hydroxyl radical reactant and loses a hydrogen (a D atom in this case) from the ring. Investigation of OH + cyclohexene-4,4,5,5-d4 confirms this result and allows mass discrimination of different abstraction pathways. Products of 2-hydroxycyclohexyl-d(10) reaction with O-2 are observed upon adding a large excess of O-2 to the OH + C6D10 system.