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

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 O-2 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 Co-2 with molecular oxygen. One reaction channel has been evidenced through reaction of Co-2 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 Co-2(16) O-2, Co-2(18) O-2 and Co-2(16) (OO)-O-18 isotopic data for five fundamental and three combination transitions enable determination of all fundamental vibrations for matrix-isolated Co-2 O-2 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 +/- 5degrees OCoO bond angle. In comparison with the CoO diatomic molecule, this suggests a near square-planar structure with a 1.765 +/- 0.01 Angstrom CoO bond distance.