Reactivity of cobalt dimer and molecular oxygen in rare gas matrices. IR spectrum, photophysics and structure of Co2O2

Abstract

The reactivity of cobalt dimer towards molecular oxygen has been investigated in rare gas matrices. If the formation of Co₂O₂ from the condensation of effusive beams of Co and O₂ in neon and argon matrices is observed after sample deposition, our results show that the in situ formation does not result from the reaction of ground state Co nor Co₂ with molecular oxygen. One reaction channel has been evidenced through reaction of Co₂ in excited states, close or above the dissociation limit. Two metastable states of Co₂O₂ with low-symmetry structures, stabilized by interaction with the matrix cage have also been evidenced between 1.4 and 2 eV above the ground state. Observation of Co₂¹⁶O₂, Co₂¹⁸O₂ and Co₂¹⁶O¹⁸O isotopic data for five fundamental and three combination transitions enable determination of all fundamental vibrations for matrix-isolated Co₂O₂ in its cyclic ground state. Semi-empirical harmonic potential calculations lead to estimates of 2.435 N cm⁻¹ for the Co–O bond force constant, and 93 ± 5° OCoO bond angle. In comparison with the CoO diatomic molecule, this suggests a near square-planar structure with a 1.765 ± 0.01 Å CoO bond distance.