Ab Initio Potential Curve for the X 3Σg− State of O2

Abstract

Using a $\text{4s2p1d}$ set of contracted Slater functions on each atom, configuration interaction (CI) wavefunctions have been calculated at eight points to determine a potential curve for the ground state of O₂. The approximate first‐order wavefunctions include 128 configurations of three basic types, and convergence to an optimum set of orbitals is attained using the Bender–Davidson iterative natural orbital procedure. Using this approach, the molecule dissociates properly to two oxygen atoms of slightly better than Hartree–Fock accuracy. The ab initio dissociation energy is 4.72 eV, compared to the Hartree–Fock value 1.43 eV and the experimental value 5.21 eV. Other computed spectroscopic constants (with experimental values in parentheses) are also in good agreement with experiment: $r_e{\text{\hspace{0.17em}=\hspace{0.17em}1.220 Å (1.207), ν}}_e\text{\hspace{0.17em}=\hspace{0.17em}1614}{\mathrm{cm}}^{\text{−1}}\text{(1580),}\mathrm{and}{B}_e\text{\hspace{0.17em}=\hspace{0.17em}1.417}{\mathrm{cm}}^{\text{−1}}\text{(1.446)}$ . Some general conclusions are drawn on the ab initio calculation of bondlengths.