Size-selected anion photoelectron spectroscopy and density functional theory study of MnC_n^−/0 (n = 3-10): Odd-even alternation and linear-cyclic structure competition

The structural and electronic properties of MnC_n⁻ (n = 3-10) clusters have been investigated using size-selected photoelectron spectroscopy and density functional theory calculations. The vertical detachment energies of MnC_n⁻ exhibit a strong odd-even alternation with increasing number of carbon atoms: the vertical detachment energies of MnC_n⁻ containing even number of carbon atoms are higher than those of adjacent ones containing odd number of carbon atoms. The theoretical analyses indicate that the spin multiplicities and relative stabilities of MnC_n^−/0 also exhibit odd-even alternations. It is found that MnC₃⁻ has three degenerate isomers with two linear structures in different electronic states and one fanlike structure. For n = 4-6, 8, and 10, the ground state structures are all linear with the Mn atom at one end. MnC₇⁻ and MnC₉⁻ have cyclic structures. As for the neutral species, MnC₃ and MnC₄ adopt fan-shaped structures, MnC₅ has a linear structure, and MnC_6-10 have cyclic configurations. The atomic dipole moment corrected Hirshfeld population analysis shows that the electrons transfer from the Mn atom to the C_n units. The total spin magnetic moments of MnC_n^−/0 (n = 3-10) clusters are mainly contributed by the local magnetic moments on the Mn atom.