Abstract: We have investigated the electronic structure and potential energy curve of molecule Mo_2 using ECP ab initio method at SCF and CI levels. Relativistic effective core potential have been used for molybdenum. It is found that the ground state of Mo_2 is
~1Σ_g~+: 1σ_g~2 1π_u~4 1δ_g~4 2σ_g~2.
It is predicted that the bond length are 1.75 and 2.01 at SCF and SCF+CI, respectively, and dissociation energy are 10.3 eV and 5.2 eV. As bond length increase, the correlation energy increase rapidly, and got a reasonable dissociation procedure at SCF+Cl level.