Abstract: The energies, equilibrium geometries and harmonic frequencies of three electronic states (the ground state X ¹Σ⁺, the first degenerate state A ¹Π and the second state B ¹Σ⁺）of BH molecule have been calculated using the GSUM (group sum of operators) method of SAC/ SAC-CI with the basis sets D95++, 6-311++g and cc-PVTZ. Comparing among the above mentioned three basis sets, the conclusion is gained that the basis set cc-PVTZ is the most suitable for the energy calculation of BH molecule. The whole potential curves for these three electronic states are further scanned using SAC/cc-PVTZ method for the ground state and SAC-CI/cc-PVTZ methods for the excited states, then having a least square fitting to Murrell-Sorbie function, and last the spectroscopy constants (Be, αe, ωe, andωeχe) are calculated, which are in better agreement with the experimental data. It is believed that Murrell-Sorbie function form and SAC/ SAC-CI method are suitable not only for the ground state, but for the low-lying excited states as well.

Key words: Atomic and molecular physics, Molecular structure and potential function, BH, Excited state, Murrell-Sorbie function