Enhanced UV emissions are reported in a flowing afterglow of active nitrogen and undischarged oxygen, when discharged oxygen is added. Enhancement of the N-2 second positive band system fluorescence, N-2(C(3)Pi(u), v' -> B(3)Pi(g), v") + hv, is reported for the first time in active N-2 + O-2. Interpretation and ramifications of N-2(C(3)Pi(u) -> B(3)Pi(g)) fluorescence increase in a nitrogen afterglow due to excited O-2 are reported on. It is deduced that the well-known metastable energy donor, N-2(A(3)Sigma(u)(+)), is also an efficient energy acceptor from excited O-2. In addition, this work leads to determination of a rate constant estimate for the reaction {N-2(A(3)Sigma(u)(+)) + O-2(a(1)Delta(g)) 1, as well as to different interpretations of observations in various research areas. (c) 2005 Elsevier B.V. All rights reserved.