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Criegee intermediates (CIs) are of great significance to Earth’s troposphere – implicated in altering the tropospheric oxidation cycle and in forming low volatility products that typically condense to form secondary organic aerosols (SOAs). As such, their chemistry has attracted vast attention in recent years. In particular, the unimolecular decay of thermal and vibrationally-excited CIs has been the focus of several experimental and computational studies, and it now recognized that CIs undergo unimolecular decay to form OH radicals. In this contribution we reveal insight into the chemistry of CIs by highlighting the hitherto neglected multi-state contribution to the ground state unimolecular decay dynamics of the Criegee intermediate products. The two key intermediates of present focus are dioxirane and vinylhydroperoxide – known to be active intermediates that mediate the unimolecular decay of CH2OO and CH3CHOO, respectively. In both cases the unimolecular decay path encounters conical intersections, which may play a pivotal role in the ensuing dynamics. This hitherto unrecognized phenomenon may be vital in the way in which the reactivity of CIs are modelled and is likely to affect the ensuing dynamics associated with the unimolecular decay of a given CI.