All-electron ab initio investigations of the three lowest-lying electronic states of the RuC molecule

The three lowest-lying electronic states of RuC, 1Σ+, 3Δ, and 1Δ, have been investigated by performing all-electron ab initio multi-configuration self-consistent-field (CASSCF) and multi-reference configuration interaction (MRCI) calculations including relativistic corrections. The electronic ground state is derived as 1Σ+ with the spectroscopic constants re=1.616 Å and ωe=1085 cm−1. The lowest-lying excited state, 3Δ, has re=1.632 Å, ωe=1064 cm−1, and Te=912 cm−1. These results are consistent with recent spectroscopic values. The chemical bonds in all three lowest-lying states are triple bonds composed of one σ and two π bonds.