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, FeO 2, FeO 3, FeO 4, Fe 2 O, Fe 2 O 2, and Fe 2 O 4 molecules, which are identified from oxygen isotopic shifts and multiplets in matrix infrared spectra. The Fe + O 2 reaction gives symmetrical bent, symmetrical cyclic, and asymmetrical bent FeO 2 isomeric products with triplet, triplet, and quartet isotopic absorptions, respectively, using statistically mixed 16,18 O 2 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(O 2 ) 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 Fe 2 O 2 absorbs at 517.4 cm -1 . Evidence is presented for isomers of FeO 3, FeO 4, and Fe 2 O 4 . Density functional theory was used to calculate energies, structures, and frequencies for product molecules to support their identification.