InCH4–H2mixture dc discharges, theCH2radicals are identified from hot H atom laser-induced fluorescence Doppler spectral profiles. We examine the possible contributions of hydrocarbon species present in the discharge, which could be dissociated by the laser photons and produce the fast H atom fragments responsible for these profiles. The dissociation energy, 4.2±0.2 eV, experimentally determined indicates that we detect mainlyCH2radicals. At a pressure of 2 Torr and a discharge current intensity of 10 mA, we show that theCH2radical density increases almost linearly with the percentage—until 15&percent;—ofCH4in the gas mixture, while the population density of the H atoms created in the plasma remains quasiconstant, except in the cathode sheath. ©1997 American Institute of Physics.