The product branching ratios for NO+(X 1 Sigma(+)) and NO+(a (3)Sigma(+)) produced from the reaction of N+ with O-2 have been measured at 298 and 500 K in a selected ion flow tube. Approximately 0.5% of the total products are in NO+(a) at both temperatures, despite the fact that the reaction to form NO+(a) is 0.3 eV exothermic. High-level ab initio calculations of the potential energy surfaces for the N+ + O-2 reaction show that the reaction from N+(P-3) + O-2((3)Sigma(g)) reactants starts with an efficient early stage charge transfer to the N(D-2) + O-2 +(X (2)Pi) channel, which gives rise to the O-2(+) (X 2 Pi) product and, at the same time, serves as the starting point for all of the reaction channels leading to NO+ and O+ products. Pathways to produce NO+(a (3)Sigma(+)) are found to be less favorable than pathways leading to the major product NO+(X (1)Sigma(+)). Production of N(D-2) has implications for the concentration of N(D-2) in the mesosphere.