Electronic structure and chemical bonding in the ground states of Tc₂ and Re₂

Abstract

Multiconfiguration second-order perturbation theory, including relativistic effects and spin–orbit coupling, has been employed to investigate the nature of the chemical bonding in the ground state of Tc₂ and Re₂. The Tc₂ ground state is found to be a state, with an effective bond order (EBO) of 4.4, and a dissociation energy of 3.25 eV. The Re₂ ground state is a 1 _g state, with EBO = 4.3. Almost degenerate to it, is a state (T _e = 77 cm⁻¹), with EBO = 4.1. Experimental evidence also indicates that the ground state is of 1 _g nature. The dissociation energy is computed to be 5.0 eV in agreement with an experimental estimate of 4 ± 1 eV.

Keywords:

• transition metal bonding
• transition metal diatoms
• ground state
• CASPT2

Acknowledgements

JPG is grateful to FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil) for a graduate fellowship. ACB acknowledges CNPq (Conselho Nacional de Desenvolvimento Científico and Tecnológico, Brazil) and FAPESP. BOR acknowledges the financial support by the Swedish Research Council (VR) through the Linnaeus Center of Excellence on Organizing Molecular Matter (OMM).