Electronic structure of Ge2 and Ge2− and thermodynamic properties of Ge2 from all electron ab initio investigations and Knudsen effusion mass spectroscopic measurements Original Research Article

The low-lying states of the molecule Ge2 and of the ion Ge2− have been investigated by all electron ab initio multi-configuration self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) calculations. The relativistic corrections for the Darwin contact term and for the mass–velocity term have been determined in perturbation calculations. Treatment of the spin-orbit coupling has been included. The ground state of Ge2 is derived as 0g+(3Σg−) with equilibrium distance 2.422 Å, and vibrational frequency 270 cm−1. The spectroscopic constants of 15 excited states are presented. Thermal functions based on the theoretically determined molecular parameters were used to derive the thermodynamic properties of the Ge2 molecule from new mass spectrometric equilibrium data. The literature value for the dissociation energy of Ge2 has been re-evaluated. The recommended dissociation energy, D∘0(Ge2), and enthalpy of formation, ΔfH∘298.15(Ge2), in kJ mol−1 are 260.7±6.8 and 484.8±6.8, respectively.