Reactions of laser-ablated iron atoms with oxygen molecules in condensing argon. Infrared spectra and density functional calculations of iron oxide product molecules

Reaction of laser-ablated Fe atoms with oxygen molecules in a condensing argon stream produced FeO, FeO₂, FeO₃, FeO₄, Fe₂O, Fe₂O₂, and Fe₂O₄ molecules, which are identified from oxygen isotopic shifts and multiplets in matrix infrared spectra. The Fe + O₂ reaction gives symmetrical bent, symmetrical cyclic, and asymmetrical bent FeO₂ isomeric products with triplet, triplet, and quartet isotopic absorptions, respectively, using statistically mixed ^16,18O₂ as the reagent. The major reaction product symmetrical bent OFeO iron dioxide molecule (150 ± 10°) is characterized by stretching fundamentals at 945.8 and 797.1 cm^-1, and the asymmetric bent FeOO form exhibits a 1204.5 cm^-1 absorption. The cyclic isomer Fe(O₂) produced spontaneously during annealing in solid argon absorbs at 956.0 cm^-1. Oxygen and iron isotopic absorptions show that FeOFe is a symmetrical bent (140 ± 10°) molecule. Rhombic Fe₂O₂ absorbs at 517.4 cm^-1. Evidence is presented for isomers of FeO₃, FeO₄, and Fe₂O₄. Density functional theory was used to calculate energies, structures, and frequencies for product molecules to support their identification.