| Abstract
| - The reactivity of atomic cobalt toward molecular oxygen in rare gas matrices has been reinvestigated.Experiments confirm that Co atoms in their a4F ground state are inert toward O2 in solid argon and neon butreactive in the b4F first excited state, in agreement with the previous gas-phase study of Honma and co-workers. The formation of CoO2 starting from effusive beams of Co and O2 has been followed by IR absorptionspectroscopy, both in neon and argon matrices. Our observations show that only the dioxo form, OCoO, isstabilized in the matrix and that IR absorptions previously assigned to the peroxo and superoxo forms are dueto other, larger species. The present data strongly support the linear geometry in rare gas matrices proposedby Weltner and co-workers. We report on measurements on all IR-active fundamental modes for 16OCo16O,18OCo18O, and 16OCo18O with additional combination transitions supplying anharmonicity correction. Thisallows for a 5.93 ± 0.02 mdyne/Å CoO harmonic bond force constant in solid neon. Using the empiricalrelationship previously optimized for the CoO diatomics, an approximate value for the CoO internuclearbond distance is proposed (1.615 ± 0.01Å). In light of recent theoretical studies predicting 2A1 or 6A1 electronicground states, the geometry and electronic structure of the OCoO molecule has also been reconsidered.Calculations carried out at the CCSD(T)/6-311G(3df) level indicate a linear structure with an re = 1.62 Åbond distance, consistent with the experimental estimate. For later studies of larger systems, where CCSD(T)calculations become too time-consuming, an effective DFT-based method is proposed which reproduces thebasic electronic and geometrical properties of cobalt dioxide. Quantitative results are compared to theexperimental data and high-level results regarding bond length and frequencies. This DFT method is used topropose a reaction pathway.
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