Direct characterization of Criegee intermediate in ozonolysis reaction of alkene

Abstract

Criegee intermediates (CIs) are the key intermediates in the ozonolysis reactions of alkenes, which are important in tropospheric oxidn. CIs are the precursors of OH radicals in the ozonolysis reactions of alkenes, and they react with many important atm. species such as SO_2, NO_2, O_3, and water, which lead to the secondary org. aerosol (SOA) formation. While several CIs have recently been synthesized from photolysis of iodoalkanes in the presence of O_2, no unambiguous observation of CIs has been made previously in the ozonolysis reactions of alkenes. This work is the first time direct observation of the gas-phase Criegee intermediate in the ozone and alkene reaction system. (CH_3)_2COO has been directly detected in the ozone and tetramethylethylene (TME) reaction using vacuum UV (VUV) photoionization mass spectrometry coupled with a fast flow reactor. Photoionization efficiency (PIE) curve has identified CI, its isomers, its decompn. products, and other products in this reaction. Chem. reaction kinetics and modeling have been carried out in the short time range of tens of milliseconds, which provides detailed reaction mechanism of the early steps of the alkene ozonolysis reaction. This study of the TME ozonolysis reaction could open a door to exploring many other Criegee intermediates in the atm. ozonolysis reactions of alkenes.