Photoelectron spectroscopy of iron carbonyl cluster anions (Fe_n(CO)^-_m, n = 1-4)

Photoelectron spectra of iron-carbonyl cluster anions (Fe_n(CO)^-_m) were measured in the gas phase at the photon energy of 4.66 eV, using a magnetic bottle electron spectrometer. The iron-carbonyl cluster anions were produced by slow electron attachment of less than 1 eV to a supersonic expansion of Fe(CO)₅ seeded in a He carrier gas. The photoelectron spectra of the Fe_n(CO)^- _5n-1 anions show unresolved broad features, and the threshold energy (E_T) and the vertical detachment energy (VDE) were determined: The E_T of Fe_n(CO)^-_5n-1 gradually increases by 0.1-0.3 eV with the cluster size. The study suggests that the iron carbonyl cluster anions produced are van der Waals clusters, in which Fe(CO)^-₄ works as an ion core.