Laser-ablated molybdenum and tungsten atoms were reacted with dioxygen and O-18-substituted dioxygen. The products of these reactions were isolated in solid argon matrices at 10 K and studied by matrix infrared spectroscopy. Analysis of spectra enabled identification of reaction products, which included MoO2, (O-2)MoO2, MoO3, WO, WO2, (O-2)WO2, and WO3. Resolution of isotopic splitting due to natural isotopic abundance of the metal verified the presence of a single metal atom in these molecules and allowed for calculation of bond angles for the molybdenum and tungsten dioxide molecules and their dioxygen complexes.