Alkene ozonolysis is a primary oxidation pathway for alkenes, the most abundant organic compounds emitted into the Earth’s troposphere after methane, and also an important source of atmospheric hydroxyl (OH) radicals. Alkene ozonolysis takes place through a complicated reaction pathway with multiple intermediates and barriers on the way to OH radicals and other products. A carbonyl oxide species, known as the Criegee intermediate (RR¢COO), represents a critical branching point on the pathway that controls the products formed in this important class of reactions. Recent studies in this laboratory are focused on four-carbon Criegee intermediates, including unsaturated methyl vinyl ketone oxide (MVK-oxide) and methacrolein oxide (MACR-oxide) derived from isoprene ozonolysis. The Criegee intermediates are generated by alternative synthetic routes, characterized utilizing infrared and ultraviolet spectroscopic methods, and probed to examine the resultant dynamics. Infrared ‘fingerprint’ and electronic spectra reflecting p-conjugation of the Criegee intermediates are obtained, along with time- and energy-resolved studies of their unimolecular decay to OH radical products. The conformation and nature of the substituents (R, R¢) of the Criegee intermediates are found to have a profound effect on their reaction dynamics. Complementary experiments under thermal conditions reveal the first direct kinetic measurements of MVK-oxide reactions with key tropospheric species and, along with theoretical modeling, provide insights on the impact of Criegee intermediates in the atmosphere.
20.04.2020 at University of Gottingen; time will soon be notified
22.04.2020 at Humboldt University of Berlin at 5 pm
27.04.2020 at Fritz Haber Institute of the Max Planck Society at 11 am
28.04.2020 at Wilhelm-Ostwald-Institute for Physical and Theoretical Chemistry, University of Leipzig at 5 pm