Theoretical studies of oxygen rings: Cyclotetraoxygen, O4

Abstract

An analogy is constructed between the known composition of elemental sulfur (principally S8 rings) and the unknown oxygen rings. Due to the weakness of O–O single bonds, as in hydrogen peroxide, it is hypothesized that oxygen rings are potential high energy density materials. A particularly attractive candidate is the O4 molecule, for which ring strain is expected to provide further destabilization relative to two separated O2 molecules. To pursue these qualitative suggestions, ab initio molecular quantum mechanics has been employed. Both self-consistent field (SCF) and configuration interaction including single and double excitations (CISD) methods have been employed in conjunction with double zeta plus polarization basis sets. At the highest level of theory the nonplanar (D2d point group, O–O–O–O torsional angle 25°) equilibrium structure is predicted to lie 2.9 kcal below the planar D4h structure, which is a transition state. The infrared spectrum is predicted at the DZ+P CISD level, as well as lower levels of theory. The O4 minimum is predicted to lie ∼100 kcal/mol above the asymptotic limit of two O2 molecules.