Products of the chlorine-atom- and hydroxyl-radical-initiated oxidation of CH₃CN

FTIR smog chamber techniques were used in the first investigation of the products following oxidation of CH₃C≡N initiated by Cl atom or OH radicals in air at 296 ± 2 K. It is shown that reaction of Cl atoms with CH₃C≡N gives ^.CH₂C≡N radicals in essentially 100% yield. These radicals add O₂ to form the peroxy radical N≡CCH₂O₂^.. Self-reaction of the peroxy radicals gives the alkoxy radical N≡CCH₂O^. which reacts exclusively with O₂ to give HC(O)C≡N (formyl cyanide). The reaction of Cl atoms with HC(O)C≡N proceeds with a rate constant of (7.0 ± 1.0) × 10^-13 cm³ molecule^-1 s^-1 via H-abstraction to give ^.C(O)C≡N radicals which add O₂ to give N≡CC(O)OO^. radicals. The subsequent chemistry of these radicals leads to the production of HC≡N and CO₂ or the acyl peroxy nitrate N≡CC(O)OONO₂, the IR spectrum of which is reported here. The reaction of OH radicals with CH₃C≡N in 700 Torr of air gives HC(O)C≡N in (40 ± 20)% yield implying that up to half of the OH + CH₃C≡N reaction could proceed via H-atom abstraction, with the remaining fraction proceeding via addition to the -C≡N group. These results are discussed in terms of the atmospheric oxidation mechanism of CH₃C≡N.