The formation of the cold hetero-nuclear alkali dimers molecules has gained great interest in the past year of both experimental and theoretical researches involved in collision dynamics, photo- associative spectroscopy, and laser cooling and trapping of alkali atoms. Recent successes in the production of Bose-Fermi ensembles of various hetero- nuclear alkali-metal dimers and dual Bose-Einstein condensates have created further interest in studies of binary mixture. The NaRb molecule is one of the promising candidates for the formation of two species Bose-Einstein condensate. This molecule has been the subject of many spectroscopic studies during the last decade. In this book, the low-lying electronic states of the molecule NaRb are investigated, taking into consideration the spin-orbit (SO) coupling and by an improved ab-initio pseudo-potential method.