Size-selected anion photoelectron spectroscopy and density functional theory calculations of ferromagnetic Fe₂C^-/0 (n...

The structural and electronic properties of iron carbide clusters Fe₂C^-/0 (n = 2-6) were investigated using size-selected anion photoelectron spectroscopy and theoretical calculations. The adiabatic and vertical detachment energies of Fe₂C^- (n = 2-6) were obtained from their photoelectron spectra. The ground state structures of Fe₂C^- (n = 2-6) were determined by comparing the theoretical results with the experimental data. The most stable isomers of Fe₂C^- adopt planar structures, except for Fe₂C₅^-, in which the carbon atoms deviate slightly from the plane. The ground state structures of neutral Fe₂C 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^- clusters are 7μ_B for even sizes and 5μ_B for odd sizes, whereas those of neutral Fe₂C 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^- exhibit odd-even alternations.