Ab initio calculation of the electronic structures of the Φ3 ground and Φ5 excited states of CoH

Abstract

The electronic structures and the spectroscopic constants of the electronic ground Φ3 and low-lying Φ5 electronic excited states of the CoH molecule were studied by multireference single and double excitation configuration interaction (MR-SDCI)+Davidson’s correction (Q) calculations and size-consistent multireference coupled pair approximation (MRCPA) calculations. Calculations were performed under C∞v symmetry using Slater-type basis functions. The electronic ground state was confirmed to be the Φ3 state. It was found that at least four reference configurations were needed to describe the ground Φ3 state correctly at the MR-SDCI+Q level, while the Φ5 state can be described well by one reference configuration, namely, the Hartree-Fock configuration. Larger dynamical electron correlation for the low-spin Φ3 state than that for the high-spin Φ5 state is discussed. Spectroscopic constants, i.e., equilibrium bond lengths (re), harmonic frequency (ωe), and excitation energy, obtained by the MR-SDCI+Q method showed good correspondence with experimental values. MRCPA calculations gave a slightly shorter value for re than experimental values, but improved ωe and the excitation energy bringing them very close to experimental values.