Spectroscopic constants and the interaction between rare-gas and open and closed shell halogen have been studied in detail using CCSD(T) method. The spectroscopic constants have been calculated using our recently developed method for the weakly bound van der Waals molecules that obey Lennard-Jones (L-J) potential. Both neutral and anionic van der Waals molecules have been investigated. The results have been compared with the theoretical and experimental values wherever available. Most of the spectroscopic constants are first reported. The nature of force between the two interacting atoms of neutral and anionic systems has been calculated and their stability has been analyzed. (C) 2008 Elsevier B.V. All rights reserved.