Observation and Photoelectron Spectroscopic Study of Novel Mono- and Diiron Oxide Molecules: FeO y - ( y = 1−4) and Fe 2 O y - ( y = 1−5)

We study novel iron oxide molecules involving one and two iron atoms by anion photoelectron spectroscopy at 3.49 and 4.66 eV photon energies. Vibrationally resolved photoelectron spectra and low-lying excited states are obtained for FeO y - ( y = 1−4) and Fe 2 O y - ( y = 1−5). In both series, the photoelectron spectra become particularly sharp and better resolved for the higher oxides, FeO 3 -, FeO 4 -, Fe 2 O 4 -, and Fe 2 O 5 - . The electron affinity of the neutral oxide molecules is observed to increase with the number of oxygen atoms, suggesting a sequential oxidation behavior. For the monoiron oxide series, an oxidation saturation is observed as evidenced by the leveling-off of the electron affinity from FeO 3 to FeO 4 . The structures and chemical bonding of these oxide molecules are discussed based on the sequential oxidation behavior. Isomers involving possibly O 2 or O 3 complexes are also observed for the diiron oxides above Fe 2 O.