Size-selected anion photoelectron spectroscopy and density functional theory calculations of ferromagnetic Fe2Cn−/0 (n = 2–6) clusters

Abstract

The structural and electronic properties of iron carbide clusters Fe₂C_n^−/0 (n = 2–6) were investigated using size-selected anion photoelectron spectroscopy and theoretical calculations. The adiabatic and vertical detachment energies of Fe₂C_n⁻ (n = 2–6) were obtained from their photoelectron spectra. The ground state structures of Fe₂C_n⁻ (n = 2–6) were determined by comparing the theoretical results with the experimental data. The most stable isomers of Fe₂C_n⁻ adopt planar structures, except for Fe₂C₅⁻, in which the carbon atoms deviate slightly from the plane. The ground state structures of neutral Fe₂C_n clusters are generally similar to their corresponding anions, except for Fe₂C₃, which adopts a planar cyclic structure containing a C₃ unit. The magnetic moments of the Fe₂C_n⁻ clusters are 7μ_B for even sizes and 5μ_B for odd sizes, whereas those of neutral Fe₂C_n are 8μ_B (6μ_B for n = 2) for even sizes and 6μ_B for odd sizes. The magnetic moments primarily originate from Fe atoms. The Fe–Fe bond lengths increase gradually with the growth of the cluster size, resulting in the transition from double-bond to single-bond character. The spin multiplicities and relative stabilities of Fe₂C_n⁻ exhibit odd–even alternations.