The reaction N-2(+)+N-2 -> N-3(+)+N from thermal to 25 eV

The endothermic reaction N-2(+)+N-2-->N-3(+)+N has been investigated both e xperimentally and by ab initio calculations. Integral cross sections are pr esented as a function of collision energy. For excited N-2(+) ions the reac tion onset shifts towards lower energies, indicating that the internal ener gy of the reactant ions promotes the reaction. Analysis of the energy depen dence of the cross section does not allow an unequivocal determination of t he reaction endothermicity. However, calculations of the ground doublet sur face indicate that the minimum energy path from reactants to products proce eds 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 initi o methods. (C) 2001 American Institute of Physics.