A detailed ab initio study based on the CASSCF and CASPT2 methods has been carried out on the 3(2)A' potential energy surface (PES) involved in the reaction between N (D-2) and O-2 to produce O(P-3) and NO. All the stationary points have been characterised and a grid of more than 800 points has been fitted to an analytical function. This PES has been used to obtain the rate constant of this reaction at different levels of theory (statistical and quasiclassical trajectory methods, taking into account recent data of our own on other PESs involved in the reaction) and has been compared with the experimental results obtaining a good agreement. (C) 2002 Elsevier Science B.V. All rights reserved.