The NO+. N-2 cationic complex is studied using high-level ab initio calculations. The geometry is found to be a skewed T shape, with two linear stationary points corresponding to the N-O+. N-N and N-N . N-O+ configurations. At the highest level of theory, CCSD(T)/aug-cc-pVQZ//CCSD(T)/aug-cc-pVTZ, the interaction energy is estimated to be 1950 cm(-1) (5.6 kcal mol(-1)), from which a Delta H-298 interaction enthalpy value of 4.9 kcal mol(-1) was derived. By using the well-established heat of formation of NO+, it was possible to derive a standard Delta H-f(298) value of 230.4 kcal mol(-1) for NO+. N-2. In addition, the enthalpy, entropy, free energy and equilibrium constants were calculated for the dissociation of the complex, as a function of altitude, for the earth's atmosphere.