All-electron ab initio investigations of the electronic states of the NiC molecule

The low-lying electronic states of NiC are investigated by all-electron ab initio multi-configuration self-consistent-field (CASSCF) calculations including relativistic corrections. The electronic structure of NiC is interpreted as perturbed antiferromagnetic couplings of the localized angular momenta of 4Fg Ni+ and 4Su C−. The predicted ground state, 1Σ+, is well separated from the dense manifold of excited states by an energy gap of 6465 cm−1. Multi-reference configuration-interaction (MRCI) calculations result in re=1.621 Å and ωe=874 cm−1 agreeing well with new experimental data by Brugh and Morse. De is determined as 2.76 eV, and D0 as 2.70 eV.