CASSCF (complete active space self-consistent field) and CASPT2 (multiconfiguration second-order perturbation theory) calculations with the cc-pVTZ and cc-pVQZ basis sets were carried out for exploring the mechanisms of the N-3 + F --> NF((1)Delta) + N-2 (i) and N-3 + F --> NF((3)Sigma) + N-2 (ii) reactions. The CASSCF and CASPT2 calculations indicate that channel (i) occurs in the (1)A' potential energy surface (PES) and along the reaction path there exists an intermediate [IM ((1)A')] followed by a transition state and that channel (i) is energetically feasible. The CASSCF calculations indicate that channel (ii) occurs in the (3)A" PES and it has a single step with a transition state [TS((3)A")], but the CASPT2 single-point calculations imply that TS((3)A") may not exist. The (1)A' and (3)A" PES crossing was explored by performing conical intersection and spin-orbit coupling calculations at the CASSCF level and the calculations imply that the crossing may not cause predissociation of IM((1)A') into the triplet ground state product. (C) 2004 Elsevier B.V. All rights reserved.