The endothermic reaction N-2(+)+N-2-->N-3(+)+N has been investigated both experimentally and by ab initio calculations. Integral cross sections are presented as a function of collision energy. For excited N-2(+) ions the reaction onset shifts towards lower energies, indicating that the internal energy of the reactant ions promotes the reaction. Analysis of the energy dependence of the cross section does not allow an unequivocal determination of the reaction endothermicity. However, calculations of the ground doublet surface indicate that the minimum energy path from reactants to products proceeds through strongly bent geometries, with an endothermicity equivalent to the thermodynamic value of about 5 eV. For linear geometries an additional barrier of about 1 eV is found in the product channel. The structure of N-4(+) in its first excited quartet state has been also calculated by ab initio methods. (C) 2001 American Institute of Physics.