Electronic structure of Ge_2 and Ge_2~- and thermodynamic properties of Ge_2 from all electron ab initio investigations and Knudsen effusion mass spectroscopic measurements

摘要

The low-lying states of the molecule Ge_2 and of the ion Ge_2~- 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 Ge_2 is derived as 0_g~+(~3∑_g~-) with equilibrium distance 2.422 A, 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 Ge_2 molecule from new mass spectrometric equilibrium data. The literature value for the dissociation energy of Ge_2 has been re-evaluated. The recommended dissociation energy, D°_0(Ge_2), and enthalpy of formation, △_fH°_(298.15) (Ge_2), in kJ mol~(-1) are 260.7 ± 6.8 and 484.8 ± 6.8, respectively.