The reactions of 4d transition metal ions (except Tc and Cd) with N2O on two potential energy surfaces, producing the metal oxide ion and N-2, are studied by means of density functional theory. The results indicate that the lowest energy path corresponds to the eta(1)(O) coordination of N2O followed by the insertion of M+ into the N-O bond. The reaction mechanism between 4d transition metal ions and N2O is an insertion-elimination mechanism. All products are formed in exothermic processes. The potential energy curve crossings, which dramatically affect reaction mechanisms, are discussed in detail. (c) 2006 Elsevier B.V. All rights reserved.