Hosted by: Trevor Sears

Carbonyl oxides, known as Criegee intermediates, are reactive radicals formed via alkene ozonolysis that are thought to play an important role in tropospheric chemistry, including reactions that lead to aerosol particle formation. Globally, reaction with water (or water dimer) is thought to be the major sink for formaldehyde oxide (CH2OO), while larger species tend to undergo thermal unimolecular decomposition (Osborn and Taatjes, 2015). However, reactions of CH2OO with trace atmospheric species can be locally competitive under certain conditions. We have applied broadband transient absorption spectroscopy (Foreman et al., 2015) to probe CH2OO via the B-1A′–X-1A′ transition in the near UV to directly measure rate constants for the reactions of CH2OO with inorganic acids and alcohols. Reaction with nitric acid (HNO3) in particular is exceptionally fast, indicating that it may be competitive with water in polluted urban areas, particularly under conditions of lower relative humidity and lower temperature (Foreman et al., 2016). The experimental measurements are supported by complementary ab initio that identify likely products and elucidate mechanistic details.