Low temperature rate coefficients for the reactions of CN and C2H radicals with allene (CH2CCH2) and methyl acetylene (CH3CCH)

Using a continuous flow CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus, rate coefficients have been measured for the reactions of the cyanogen (CN) and ethynyl (C2H) radicals with allene (CH2CCH2) and methyl acetylene (CH3CCH) at temperatures from 295 down to 15 K for the reactions of CN and down to 63 K for those of C2H. All four reactions occur at rates close to the collision-determined limit. The results are compared with those obtained earlier for the reactions of other alkenes and alkynes, and, in the accompanying Letter by Vakhtin et al., with results for C2H+CH2CCH2 and C2H+CH3CCH obtained at 103 K using a pulsed Laval apparatus. The implications of these latest results for the chemistry of interstellar clouds and planetary atmospheres are discussed.