Reaction of laser-ablated CuCl molecules with dioxygen upon condensation in excess argon results in IR absorption at 1175.0 cm(-1), which is assigned to the O-O stretching vibration of the ClCu(O-2) molecule based on isotopic substituted experiments. DFT calculations predicted a B-3(1) ground state ClCu(O-2), in which the O-2 unit possesses a eta(2) binding mode to the metal center with C-2v symmetry. Similar results were obtained in laser-ablated NiCl and O-2 reactions. The O-O stretching vibration of the (4)A(1) ground state ClNi(O-2) molecule was observed at 1097.7 cm(-1) in solid argon.