Interaction between two Co atoms. An all electron ab initio HF–CI investigation

Abstract

In the present work we present all electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of the 84 low‐lying electronic states resulting from the interaction between two Co atoms in the 4F(3d)8(4s)1 term. The basis set used was of double zeta quality in general, but the 3d orbital was represented by a triple zeta function. The calculations were performed to the same degree of accuracy for all 84 states. The predicted 5Σ+ g ground state of the Co2 molecule is due to the natural orbital occupation (3dσ g )2.00(3dπ u )3.09(3dδg)3.02 (3dδ u )2.98(3dπg)2.91(3dσ u )2.00 (4sσ g )1.94(4sσ u )0.06. From our calculated spectroscopic data of the Co2 molecule, we have estimated the equilibrium distance to be 4.6 a.u. and the vibrational frequency as 240 cm− 1. The chemical bond between the Co atoms is a single bond almost entirely due to the 4sσ g molecular orbital. The 84 low‐lying electronic states make a large contribution to the partition function, resulting in a lowering of the experimental dissociation energy of the Co2 molecule. Reevaluating the data by Kant and Strauss resulted in an experimental dissociation energyD 0 0 of 22±6 kcal mol− 1 or 93±25 kJ mol− 1.