A theoretical study of the gas-phase reactions of propadiene with NO3: mechanism, kinetics and insights

Abstract

In this study, the conversion mechanisms and kinetics of propadiene (CH₂CCH₂) induced by NO₃ were researched using density functional theory (DFT) and transition state theory (TST) measurements. The NO₃-addition pathways to generate IM1 (CH₂ONO₂CCH₂) and IM2 (CH₂CONO₂CH₂) play a significant role. P3 (CH₂CONOCHO + H) was the dominant addition/elimination product. Moreover, the results manifested that one H atom from the –CH₂– group has to be abstracted by NO₃ radicals, leading to the final product h-P1 (CH₂CCH + HNO₃). Due to the high barrier, the H-abstraction pathway is not important for the propadiene + NO₃ reaction. In addition, the computed k_tot value of propadiene reacting with NO₃ at 298 K is 3.34 × 10⁻¹⁵ cm³ per molecule per s, which is in accordance with the experimental value. The computed lifetime of propadiene oxidized by NO₃ radicals was assessed to be 130.16–6.08 days at 200–298 K and an altitude of 0–12 km. This study provides insights into the transformation of propadiene in a complex environment.