Size-selected anion photoelectron spectroscopy and density functional theory calculations of ferromagnetic Fe₂C_<i>n</i>^−/0 (<i>n</i> = 2–6) clusters

The structural and electronic properties of iron carbide clusters Fe₂C_<i>n</i>^-/0 (<i>n</i> = 2-6) were investigated using size-selected anion photoelectron spectroscopy and theoretical calculations. The adiabatic and vertical detachment energies of Fe₂C_<i>n</i>^- (<i>n</i> = 2-6) were obtained from their photoelectron spectra. The ground state structures of Fe₂C_<i>n</i>^- (<i>n</i> = 2-6) were determined by comparing the theoretical results with the experimental data. The most stable isomers of Fe₂C_<i>n</i>^- adopt planar structures, except for Fe₂C₅^-, in which the carbon atoms deviate slightly from the plane. The ground state structures of neutral Fe₂C_<i>n</i> clusters are generally similar to their corresponding anions, except for Fe₂C₃, which adopts a planar cyclic structure containing a <i>C</i>₃ unit. The magnetic moments of the Fe₂C_<i>n</i>^- clusters are 7<i>μ</i>_B for even sizes and 5<i>μ</i>_B for odd sizes, whereas those of neutral Fe₂C_<i>n</i> are 8<i>μ</i>_B (6<i>μ</i>_B for <i>n</i> = 2) for even sizes and 6<i>μ</i>_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_<i>n</i>^- exhibit odd-even alternations.