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) an d multireference configuration interaction (MRCI) calculations have been ca rried out to determine the low-lying states of the molecule GeC. The electr onic ground state is predicted to be (3)Pi. Based on the results of the MRC I calculations, the equilibrium distance for the (3)Pi ground state has bee n computed as 1.842 Angstrom and the vibrational frequency as 827 cm(-1). T he ground state is separated from the excited states (3)Sigma(-), (1)Sigma( +), (1)Pi, and (1)Delta by 3552, 5768, 7322, and 8303 cm(-1), respectively. The chemical bond in the (3)Pi electronic ground state has double-bond cha racter. It is polar with charge transfer from Ge to C giving rise to a dipo le moment of 1.68 D at 1.84 Angstrom. Thermal functions as derived from the theoretical molecular parameters were used in the calculation of the therm odynamic properties of the GeC molecule from new mass spectrometric equilib rium data. Also, the literature value for the dissociation energy of GeC ha s been reevaluated. The recommended dissociation energy, D degrees(0)(GeC), and enthalpy of formation, Delta(f)H degrees(298.15)GeC), in kJ mol(-1) ar e 455.7 +/- 11 and 630.4 +/- 11, respectively.