A microwave discharge (2.45 GHz) is used to study the conversion of methane in a nitrogen afterglow. Investigations are performed both by means of emission spectroscopy and mass spectrometry.We show that methane is injected in the ‘early afterglow’ of the nitrogen discharge where the energy transfer between and is the dominant process producing . Comparing experimental to theoretical results obtained for different vibrational levels v′ of the state at different pressures, we determined the reaction rate constant values corresponding to the energy transfer between and , assuming a Treanor distribution (Tr = 400 K, Tv0–1 = 2500 K) for the vibrational levels of . The reaction rate constant values range from 1.63 × 10−18 m3 s−1 for v′ = 0 to 3.62 × 10−11 cm3 s−1 for v′ = 8. The mean value is equal to 1.93 × 10−17 m3 s−1 when v′ ranges from 0 to 10.The emission intensity decay of the first positive system is studied for bands corresponding to Δv = 3 versus methane concentration. The reaction rate constant value measured for the quenching of by CH4 is close to values proposed in literature in the case of collisions between and CH4. We studied the formation of CN, HCN and C2N2 species in the afterglow, comparing experimental to theoretical results and we measured the reaction rate constant value corresponding to:(1) The production of HCN, by reaction of CH3 with N, k9 = 8.7 × 10−18 m3 s−1.(2) The production of CN, by reaction of CHx<4 with N, γk10 = 1.2 × 10−17 m3 s−1, with γ = .(3) The production of C2N2, we show that it is probably due to the reaction between gaseous and adsorbed cyanogen radicals on the reactor wall. The product of the reaction rate constant by the surface density of CN adsorbed is equal to k14(CNs) = 55 ms−1.(4) The global destruction of CN and C2N2 when CH4 in injected in the afterglow, k11 < 1 × 10−19 m3 s−1 and k15 = 9 × 10−20 m3 s−1, respectively.