A THEORETICAL STUDY OF $^{3}\pi$ AND $^{3}\Sigma$ STATES OF $C_{2}$

Author Institution:Self-consistent field plus configuration interaction calculations of the electronic structure and properties of the lowest $^{3}\Pi$ and $^{3}\Sigma$ states of $C_{2}$ are described. The calculations used a large (46) Slater-type basis set to describe the molecular orbitals. Approximately 6,000 spin-adapted configurations were considered in the Cl calculations. The calculated properties include the dissociation energy, term energies, and the sum of the squares of the electronic transition moments, $\Sigma|R_{e}|^{2}$. The calculated dissociation energy of 6.10 eV aggress well with the experimental value of $6.25 \pm 0.20$ eV. Calculated term energies for the $b^{3}\Sigma^{-}_{g}, d^{3}\Pi_{g}$, and $e^{3}\Pi_{g}$ states are within 0.05 eV of the accepted experimental values. The $\Sigma|R_{e}|^{2}$ values for the Swan system $(a^{3}\Pi_{u} - d^{3}\Pi_{g})$, Fox-Herzberg system $(a^{3}\Pi_{u} - e^{3}\Pi_{g})$ and Ballik-Ramsay system $(a^{3}\Pi_{u} - b^{3}\Sigma^{-}g)$ have been calculated as a function of internuclear separation. These results are compared with existing experimental and theoretical data