Abstract: The energies, equilibrium geometries and harmonic frequencies of X¹∑_g⁺, A¹∑_u⁺ and B¹Ⅱ_u, of molecule Na₂ are calculated by the GSUM (Group Sum of Operators) method of SAC/SAC-CI using basis sets 6-311 ++ g, 6-311g^** and cc-PVTZ. It is found that 6-311g^** is suitable for energy calculation of molecule Na₂. The potential curves of ground states and excited states are scanned by the SAC/6-311g^** and SAC-CI/6-311g^** methods, respectively. A least square is fitted to a Murrell-Sorbie function.The spectroscopy constants (B_e, α_e, ω_e, and ω_eX_e) are calculated and show good agreement with experiment. It is believed that Murrell-Sorbie function and the SAC/SAC-CI method are suitable for ground states and for low-lying excited states as well.

Key words: molecular structure and potential function, excited state, Murrell-Sorbie function