Photoelectron spectroscopy of FeO− and FeO−2: Observation of low-spin excited states of FeO and determination of the electron affinity of FeO2

The photoelectron spectra of FeO− and FeO−2 are obtained at 3.49 eV photon energy. Transitions to the ground state (5Δ) and three low-lying excited states (5Σ+, 3Σ+, and 3Δ) of FeO are observed. The two low-spin excited states found at 6770 and 8310 cm−1 above the ground state, respectively, have not been observed before. The two Σ states, characteristic of detachment of a nonbonding electron from the FeO− anion, exhibit no vibrational progressions while a vibrational progression is observed for each of the two Δ states. The two high-spin states 5Δ and 5Σ+ are in agreement with a previous photoelectron study [P.C. Engelking and W. C. Lineberger, J. Chem. Phys. 66, 5054 (1977)]. The 3Δ state has a vibrational frequency of 800 (50) cm−1. The spectrum of FeO−2 only shows one major feature with little vibrational structure at this photon energy. The electron affinity of FeO2 is determined to be 2.358 (0.030) eV.