Mechanism and kinetics of the reaction of 1,4-thioxane with O3 in the atmosphere – A theoretical study

A comparable DFT study on reaction of CHCl•- with O3 and S2O

CONTEXT

In this discussion, we began building two model, S₂O + CHCl^•- and O₃ + CHCl^•-, using DFT-BHandHLYP method, to study their reactions mechanisms on singlet PES. For this purpose, we hope to explore the effects of the difference between sulfur and oxygen atoms on the CHCl^•- anion. Experimentalists and computer scientists may utilize the collected data to generate a wide range of hypotheses for experimental phenomena and predictions, allowing them to realize their full potential.

METHODS

The ion-molecule reaction mechanism of CHCl^•- with S₂O and O₃ was studied using the DFT-BHandHLYP level of theory with the aug-cc-pVDZ basis set. Our theoretical findings show that Path 6 is the favored reaction pathway for CHCl^•- + O₃ reaction as identified by the O-abstraction reaction pattern. Comparing to the direct H- and Cl-abstraction mechanisms, the reaction (CHCl^•- + S₂O) prefers the intramolecular S_N2 reaction pattern. Moreover, the calculated results demonstrated that the CHCl^•- + S₂O reaction is thermodynamically more favorable than the CHCl^•- + O₃ reaction, which is kinetically more advantageous. As a result, if the required reaction condition in the atmospheric process is met, the O₃ reaction will happen more effectively. In terms of kinetics and thermodynamics viewpoints, the CHCl^•- anion was very effective in eliminating S₂O and O₃.

A Computational Perspective on the Chemical Reaction of HFO-1234zc with the OH Radical in the Gas Phase and in the Presence of Mineral Dust

The gas phase and heterogeneous reaction on mineral dust aerosols of trace gases could significantly affect the tropospheric oxidation capacity and aerosol composition of the atmosphere. In this work, the OH radical-initiated oxidation of a hydrofluoroolefin, HFO-1234zc, and subsequent reaction of favorable intermediates with other reactive species, such as O₂, HO₂, and NO_x (x = 1-2) radicals, were studied, and the role of mineral dust in the form of silicate clusters on the reaction mechanism and rate constant was studied. In the gas phase, OH radical addition to HFO-1234zc is kinetically more favorable than the H-atom abstraction reaction. The calculated reaction energy barrier and thermochemical parameters show that both the initial reactions are more feasible on silicate clusters. Thus, silicates can act as chemical sinks for trapping of hydrofluoroolefins (HFOs). It is found that both gas-phase and heterogeneous reactions are responsible for the transformation of HFOs into fluorinated compounds in the atmosphere. Further, the results show that the ozone creation potential of HFO-1234zc is low, and few of the products are harmful to aquatic organisms. This study provides new insights on the formation of toxic pollutants from the oxidation of HFO-1234zc, which may have significant implications in the troposphere.