FTIR studies of the NO3 initiated degradation of but-2-yne: mechanism and rate constant determination

Abstract

The products and mechanism of the gas-phase reaction of NO₃ radicals with but-2-yne in purified air have been investigated by FTIR spectroscopy. The experiments were carried out at 298 ± 3 K and 760 ± 5 Torr in a 250 l stainless-steel reactor in which NO₃ was generated by the thermal dissociation of N₂O₅. Experiments with ¹⁵NO₃ were also performed. Products include butadione, peroxyacetyl nitrate, ketene and acetic acid. Ketene was observed to react further with NO₃ and this reaction was also investigated. The rate constants for the NO₃ reaction with but-2-yne and ketene were determined by the relative-rate method as 7.0 ± 0.8 and 10.6 ± 1.3 × 10^–14 cm³ molecule^–1 s^–1, respectively, using (E)-but-2-ene as a reference. Reaction mechanisms for the but-2-yne and the ketene degradations are proposed.