Observation and Photoelectron Spectroscopic Study of Novel Mono- and Diiron Oxide Molecules: FeOy- (y = 1−4) and Fe2Oy- (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 FeOy- (y = 1−4) and Fe2Oy- (y = 1−5). In both series, the photoelectron spectra become particularly sharp and better resolved for the higher oxides, FeO3-, FeO4-, Fe2O4-, and Fe2O5-. 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 FeO3 to FeO4. The structures and chemical bonding of these oxide molecules are discussed based on the sequential oxidation behavior. Isomers involving possibly O2 or O3 complexes are also observed for the diiron oxides above Fe2O.