The Van der Waals complex between hydroperoxy radical (HO2) and hypochlorous acid (HOCl) has been studied using the B3LYP density functional theory method, the second-order Moller-Plessett level of theory, as well as the coupled-cluster method (CCSD(T)) with basis sets as large as 6-311++G(3df, 3pd). Our calculations show stabilization energies for HO2-HOCl of 4.83, 5.03, 4.64, and 5.28 kcal/mol at the B3LYP/6-311++G(3df, 3pd), MP2/6-311++G(3df, 3pd), CCSD(T)/6-311++G(3df, 3pd) and G2 levels of theory, respectively. (c) 2005 Published by Elsevier B.V.