The ground and excited states of the Sr-2 molecule has been investigated by use of a two-valence-electron semi-empirical pseudopotential (PP(2)) and applying the internally contracted multireference Cl method (ICMRCI) and complete active space SCF (CAS SCF) reference wavefunctions. In the calculations, core polarization and core-valence correlation have been accounted for by adding a core-polarization potential (CPP) to the hamiltonian. Moreover, the single-reference coupled-cluster approach with single and double excitations including a perturbative treatment of triple excitations (CCSD(T)) has been used in ground-state calculations for Sr-2 and Sr-2(+) to yield more accurate potential curves. Spin-orbit (SO) coupling between the singlet and triplet states correlating, respectively, with the (5p)P-1 and (5p)P-3 Sr terms has been investigated using a semi-empirical two-electron SO pseudopotential. (C) 2003 Elsevier Science B.V. All rights reserved.