Electronic states and nature of bonding in the molecule MoC by all electron ab initio calculations

Abstract

In the present work all electron ab initio multiconfiguration self-consistent-field (CASSCF) and multireference configuration interaction (MRCI) calculations have been carried out to determine the low-lying electronic states of the molecule MoC. The relativistic corrections for the one electron Darwin contact term and the relativistic mass-velocity correction have been determined in perturbation calculations. The electronic ground state is predicted as Σ3−. The spectroscopic constants for the Σ3− electronic ground state and eight low-lying excited states have been derived by solving the Schrödinger equation for the nuclear motion numerically. Based on the results of the CASSCF calculations the Σ3− ground state of MoC is separated from the excited states Δ3,Σ5−,Γ3,Δ1,Π5,Σ1+ and Π3 by transition energies of 4500, 6178, 7207, 9312, 10 228, 11 639, and 16 864 cm−1, respectively. The transition energy between the Σ3− ground state and the Π3 state as derived in the MRCI calculations is 15 484 cm−1. For the Σ3− ground state the equilibrium distance has been determined as 1.688 Å, and the vibrational frequency as 997 cm−1. The chemical bond in the Σ3− electronic ground state has triple bond character due to the formation of delocalized bonding π and σ orbitals. The chemical bond in the MoC molecule is polar with charge transfer from Mo to C, giving rise to a dipole moment of 6.15 D at 3.15 a.u. in the Σ3− ground state.