Abstract The potential energy curves (PECs) of four low-lying electronic states of the P 2 molecule, X 1 Σ g + , a 3 Σ u + , b ′ 3 Σ u - and A 1 Π g , have been studied using the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with correlation-consistent basis set, aug-cc-pV6Z, in the valence range. Using these PECs, the spectroscopic parameters for these electronic states are determined and compared in detail with those of previous studies reported in the literature. The comparison shows that excellent agreement exists between the present results and the available experiments. By solving the radial Schrodinger equation of nuclear motion, the first 30 vibrational states for the four electronic states are computed when the rotational quantum number J equals zero. For each vibrational state, the vibrational level G( υ ), inertial rotation constant B υ and centrifugal distortion constant D υ are determined when J = 0, which are in good accord with the available measurements.