Harold S. Johnston Seminar in Physical Chemistry: Exploring uncharted regions of atmospheric reaction pathways

Seminar | March 6 | 4-5 p.m. | 120 Latimer Hall

 Prof. Marsha Lester, Department of Chemistry, University of Pennsylvania

 College of Chemistry

Alkene ozonolysis is a primary oxidation pathway for alkenes emitted into the troposphere and also an important source of atmospheric hydroxyl radicals. Alkene ozonolysis takes place on a reaction path with multiple minima and barriers along the way to OH products. In particular, a key reaction intermediate, known as the Criegee intermediate, R1R2COO, had eluded detection until very recently. In this laboratory, the simplest Criegee intermediate CH2OO and methyl-, dimethyl-, ethyl-, and vinyl-substituted Criegee intermediates have been generated by an alternative synthetic route, detected by VUV photoionization, and characterized on a strong * transition. Recent studies have focused on vibrational activation of Criegee intermediates in the vicinity of and at energies much below the barrier associated with hydrogen transfer that leads to OH radical products. Infrared action spectra of the Criegee intermediates are obtained, along with time-resolves rates for appearance of OH radical products following vibrational activation under collision-free conditions. Complementary theoretical calculations are carried out to predict the energy-dependent unimolecular decay rates of the Criegee intermediates. Quantum mechanical tunneling through the barrier is shown to make a significant contribution to the decay rates. The results are extended to thermally averaged unimolecular decay of stabilized Criegee intermediates under atmospheric conditions.

 Light refreshments will be served at 3:50 at The Coffee Lab

 seminarcoordinator-cchem@berkeley.edu, 510-643-0572