Executive Summary : | Criegee intermediates (CrIs) are crucial in enhancing the oxidizing capacity of the troposphere by generating non-photolytic OH radicals. They help in the formation of less volatile compounds that condense to form secondary organic aerosols. The modeling of CrIs in atmospheric chemistry has gained significant attention in recent years. CrIs are generated by [3+2] cycloaddition of ozone and alkenes in the atmosphere, which undergo various reactions due to their substantial internal energy. Experimental studies have proposed schemes for the generation of transient CrIs in the laboratory, mainly involving the generation of transient carbene by photolysis of a suitable precursor. The synthesis of NHC-carbene is significant as the nitrogen substitution stabilizes the CrIs. However, the recent identification of singlet NHC-carbene CrIs raises questions about the exact mechanism of CrIs formation in the laboratory. This proposal aims to elucidate the formation of carbene-based CrIs on the ground state and excited electronic state, examining dioxirane and spiro-dioxirane formation during the experiment. The project aims to explore the formation of the proposed NHC carbene CrIs, dioxirane, the effect of non-adiabatic effects in thermal isomerization reactions, and develop a computational strategy to calculate photo-absorption spectra and photolytic rate constant. The results will contribute significantly to understanding the electronic mechanisms of CrI formation and its unimolecular chemistry at the ground state and excited state. |