In the afterglow associated with combining N( 4S) + O( 3P) atoms, the intensities of β band emissions from NO(B 2Π)υ′ = 1,2 show a more than first order dependence on [O]. It is shown that this results from two independent mechanisms populating these levels. One is the accepted general mechanism which also populates υ′ = 0, 3 and involves the intermediate states NO(a 4Π) and NO(b 4Σ −). The other, termed the enhancement route, depends strongly upon near-resonant energy transfer processes which are the origin of its specificity. The primary step is a transfer of energy from NO(a 4Π) to N( 4S) to produce predominantly N( 2P). N( 2P) combines with O( 3P) and after energy degradation this is postulated to populate a precursor state which, after near-resonant energy transfer to O( 3P) to yield O( 1D), populates NO (B 2Π)υ′ = 1, 2. Identification of the immediate precursor as NO(B′ 2Δ) is shown to explain the specificity of the enhancement route in terms of the resonant nature of the energy transfer processes. It is shown that the intensities of β band emissions require at least 4% of N + O + M combinations to follow the enhancement route. It is also shown that energy resonance considerations explain the facts that emission from NO(B 2Π)υ′ = 0 is predominantly quenched by direct interaction of O( 3P) atoms and by interaction of N( 4S) atoms with the immediate precursor NO(b 4Σ −)υ′ = 0.