Excited State Dynamics of CH₃CHOO Criegee Intermediates in the Upper Atmosphere of the Earth

Abstract: Carbonyl oxides, or Criegee intermediates, play an important role in many physicochemical processes occurring in the Earth’s atmosphere. Criegee intermediates are chemically active compounds that easily react with other atmospheric components, promoting the formation of OH and CH₃ radicals, toxic compounds of nitrogen, and various acids. Traditionally, the literature considers reactions involving only those carbonyl oxides that are the most stable in the troposphere under the standard atmospheric conditions. In this study, it is shown that in the mesosphere and ionosphere, where the total concentration of molecules is low and the intensity of UV radiation and the number of free electrons are high, reactions involving electronically excited states of the Criegee intermediates CH₃CHOO play a significant role. In this case, we should take into account the features of the decomposition of all isomers of the CH₃CHOO molecule.