Computational study on the mechanisms and kinetics of the CH2XO2 + I (X = F、Cl、Br and I) reactions in the atmosphere

Abstract

The mechanisms, kinetics and ecotoxicity valuation of the gas-phase CH₂XO₂ (X = F、Cl、Br and I) with I reactions were investigated by using quantum chemical methods. The calculated results indicate that the title reactions could ocure on either the singlet or triplet potential energy surfaces (PES). Addition/elimination, S_N2 displacement and H-abstraction mechanisms were found on the singlet PES, and only S_N2 displacement mechanism was located on the triplet PES. The dominant reaction takes place on the singlet PES, and the primary pathway is CH₂XO₂ + I → IM1 (CH₂XOOI) → P1 (CHXO + HIO). Owing to high energy barriers and unstable products, other products generation channels could be neglected. RRKM theory was used to calculate rate constants, and the rate constant at 298 K of the CH₂IO₂ + I reaction is consistent with the experimental data. Time-dependent density functional theory (TDDFT) calaulations revealed that the primary intermediates CH₂XOOI could undergo photolysis under sunlight. CH₂XOOI and primary products CHXO (X = F, Cl, Br and I) were regard as toxic substance with potential significant hazards to three aquatic organisms.