ELECTRONIC STRUCTURE AND THERMODYNAMIC PROPERTIES OF THE MOLECULE GEC FROMALL-ELECTRON AB INITIO CALCULATIONS AND KNUDSEN EFFUSION MASS SPECTROMETRIC MEASUREMENTS

All-electron ab initio multiconfiguration self-consistent-field (CASSCF) and multireference configuration interaction (MRCI) calculations have been carried out to determine the low-lying states of the molecule GeC. The electronic ground state is predicted to be 3Π. Based on the results of the MRCI calculations, the equilibrium distance for the 3Π ground state has been computed as 1.842 A and the vibrational frequency as 827 cm-1. The ground state is separated from the excited states 3Σ-, 1Σ+, 1Π, and 1∆ by 3552, 5768, 7322, and 8303 cm-1, respectively. The chemical bond in the 3Π electronic ground state has double-bond character. It is polar with charge transfer from Ge to C giving rise to a dipole moment of 1.68 D at 1.84 A. Thermal functions as derived from the theoretical molecular parameters were used in the calculation of the thermodynamic properties of the GeC molecule from new mass spectrometric equilibrium data. Also, the literature value for the dissociation energy of GeC has been reevaluated. The recommended dissociation energy, D°0(GeC), and enthalpy of formation, ∆fH°298.15(GeC), in kJ mol-1 are 455.7 ( 11 and 630.4 ( 11, respectively.