The ground, excited, and negatively ionized states of Fe2

Abstract

The Fe2 molecule was studied by ab initio SCF and CI calculations. The basis sets as well as reference configuration state functions were carefully chosen. Results showed the ground state of the molecule to be 7Δu. The state could not be expressed as a single configuration state function. The equilibrium nuclear distance was 2.02 Å, which is close to the experimental value (1.87–2.02 Å). Resulting dissociation energy was 0.94 eV relative to 3d7 4s1 5F but −1.29 eV relative to 3d6 4s2 5D. In the anion state, an attached electron was found to be in an antibonding orbital (4pσu), and calculated electron affinity (0.45 eV) was favorably compared with the experimental value (0.90 eV). Calculations revealed the excited states to lie at 0.69 eV above the ground state, while that observed by negative ion photoelectron spectroscopy was 0.53 eV. A 20% reduction of vibrational frequency was also found in the excited and anion states. Theoretical results were in harmony with experimental ones, except for the dissociation energy value.