The low-lying electronic excited states of NiCO.

Highly correlated coupled cluster methods with single and double excitations (CSSD) and CCSD with perturbative triple excitations were used to predict molecular structures and harmonic vibrational frequencies for the electronic ground state X 1Σ+, and for the 3Δ, 3Σ+, 3Φ, 1 3Π, 2 3Π, 1Σ+, 1Δ, and 1Π excited states of NiCO. The X 1Σ+ ground state’s geometry is for the first time compared with the recently determined experimental structure. The adiabatic excitation energies, vertical excitation energies, and dissociation energies of these excited states are predicted. The importance of π and σ bonding for the Ni–C bond is discussed based on the structures of excited states.