How Does the Central Atom Substitution Impact the Properties of a Criegee Intermediate? Insights from Multireference Calculations

Complete active space self-consistent field (CASSCF) and multireference configuration interaction (MRCI)-based multireference calculations have been performed to better understand the ground state properties and the photodissociation mechanism of SiH 2 OO, a silicon analogue of the parent Criegee intermediate, CH 2 OO. The CASSCF/aug-cc-pV(T+d)Z results suggest that the ground state of SiH 2 OO is severely multireference in nature. This explains why SiH 2 OO could not be characterized in recently reported coupled cluster calculations. An important implication of this multireference character is the dramatically enhanced reactivity of SiH 2 OO, i.e., the calculated barrier for the cyclization of SiH 2 OO is only 4.4 kcal/mol, which is nearly 10 kcal/mol lower than that reported for the CH 2 OO case. The MRCI/aug-cc-pV(T+d)Z results on the evolution of the low-lying singlet electronic states along the OO bond suggest that SiH 2 OO absorbs strongly in the near UV–vis region. These results improve our fundamental understanding of the thermal and photobehavior of XH 2 OO (X = C, Si, Ge, and Sn) that serve as precursors for dioxiranes, an important class of oxidants for the synthesis of value-added chemicals, and also find their applications in optodevices.