Benzylperoxy radical cation: an exceptionally stable and bound species

The energetics of ionization and dissociation of the benzylperoxy radical have been investigated using explicitly correlated coupled-cluster methods. The theoretical values for the adiabatic ionization energy (9.331 eV) and cationic dissociation barrier (0.155 eV) harmoniously predict the elusiveness of the benzylperoxy radical in the contexts of photoionization and ion-molecule reactions. These properties make it an exception among unsaturated alkyl peroxy radicals, which typically undergo dissociative ionization. An in-depth scrutiny into the underlying electronic effects resposible for its elusiveness—predictably spanning photoionization mass spectrometry and ion-molecule reaction preparation—has profound implications, calling for a revised view of the valence bond perspective. By employing localized intrinsic bond orbital (IBO) methods in the study of the benzylperoxy radical cation, we present a case for reintroducing the Linnett double-quartet theory as the missing link between the theoretical basis and intuitive mechanisms involving triplet species, such as molecular oxygen. © 2025 The Royal Society of Chemistry.