Reactions of Laser-Ablated Cobalt Atoms with O₂. Infrared Spectra of Cobalt Oxides in Solid Argon

Laser-ablated Co atoms react with O 2 to give the linear dioxide, the monoxide, and the rhombic (CoO) 2 dimer molecules. The linear OCoO molecule is characterized by oxygen-18 substitution in strong ν 3 (945.4 cm -1 ) fundamental and weak ν 1 +ν 3 (1717.6 cm -1 ) combination bands. Annealing to 20−30 K to allow diffusion and reaction of cold cobalt atoms and dioxygen markedly increases weak bands due to the Co(O 2 ) and CoOO complexes and higher species including OOCoO, OOCoO 2, (O 2 )CoO 2, and the dimer (CoO 2 ) 2 . DFT and CASSCF calculations performed on the three CoO 2 isomers and rhombic (CoO) 2 support these assignments; DFT calculations are also presented for the rhombic (FeO) 2 molecule.