The geometry, vibrational frequencies, thermochemistry, quadrupole moments and electronic structure of C 2Na 2: Comparison with C 2Li 2, C 2H 2, C 2F 2 and C 2Cl 2

Abstract

The electronic structure of Na 2C 2 is studied using ab initio electronic structure methods and is compared to the companion molecule Li 2C 2. Both the linear D ∞ h and planar structures are minima on the ground state potential surface with the planar D 2 h conformation being the lowest energy form, similar to Li 2C 2. At the CCSD(t) level the planar form is more stable that the linear by 11.2 kcal/mol as compared with 7.34 kcal/mol for Li 2C 2. Both molecules are significantly ionic. The vibrational frequencies, atomization energy at 0 K, D 0, and the standard enthalpy of formation, Δ H 0 f are calculated and compared to those of Li 2C 2 as well as HCCH, FCCF and ClCCCl. We find D 0 and Λ H 0 f to be 331.1 and 84.92 kcal/mol for Li 2C 2 and 298.3 and 93.25 kcal/mol for Na 2C 2. We calibrate these by calculating the same quantities for HCCH, FCCF and ClCCCl.