The spectra of flowing microwave post-discharge excited in N2 and N2+CH4(N2+C2H2) gas mixtures have been studied at low temperature (77 K). The molecular spectra of CN emitted by the collision-induced N + C and N + CH chemiluminescent reactions in the low-temperature afterglow system have been thoroughly investigated. The intensity of different CN (B2SIGMA+-X2SIGMA+) vibrational bands is very sensitive to low hydrocarbon concentration in nitrogen used as the working gas. Detection of hydrocarbon species has been demonstrated from concentrations of CH4 and C2H2 in N2 greater than 10(10) molecules . cm-3.