Slow photoelectron velocity-map imaging spectroscopy of the Fe₃O⁻ and Co₃O⁻ anions.

Abstract

We report high-resolution photoelectron spectra of the transition metal suboxide clusters Fe3O(-) and Co3O(-). The combination of slow electron velocity-map imaging and cryogenic cooling yields vibrationally well-resolved spectra, from which we obtain precise values of 1.4408(3) and 1.3951(4) eV for the electron affinities of Fe3O and Co3O. Several vibrational frequencies of the neutral ground state Fe3O and Co3O clusters are assigned for the first time, and a low-lying excited state of Fe3O is observed. The experimental results are compared with density functional electronic structure calculations and Franck-Condon spectral simulations, enabling identification of the structural isomer and electronic states. As has been found in photoelectron spectra of other trimetal oxo species, Fe3O(0/-) and Co3O(0/-) are assigned to a μ2-oxo isomer with planar C(2v) symmetry. We identify the ground states of Fe3O(-) and Co3O(-) as (12)A1 and (9)B2 states, respectively. From these states we observe photodetachment to the (11)B2 ground and (13)A1 excited states of Fe3O, as well as to the (8)A1 ground state of Co3O.