Thermodynamical analysis of the atmospheric fate of the CH3SCH2O2 radical

Abstract

The thermodynamic properties of nine possible reactions for the atmospheric fate of the CH₃SCH₂O₂ radical are analysed in this work. The reactant species considered were NO, NO₂, HO₂, CH₃O₂, CH₃S, CH₃SO, CH₃SO₂, O and O₂. The calculations were performed at the UCCSD(T)/cc-pVTZ//MP2/6-31G(d) level of theory. Reactions of the CH₃SCH₂O₂ radical with NO, NO₂, HO₂, CH₃S, CH₃SO, CH₃SO₂ and O are exothermic and spontaneous. In the reaction with NO₂, the equilibrium will be highly dislocated towards the reactants. The reaction with CH₃O₂ radical is endothermic by a small quantity, but spontaneous. The estimated rate constant indicates that it will not be important. Reaction with O₂ leading to the CH₃SCH₂O and O₃ products is thermodynamically unfavourable, having a positive reaction enthalpy. The thermodynamical features of the reactions with O and HO₂ radicals indicate that these reactions should be important in this process, and kinetic studies of these reactions are strongly suggested. The heats of formation of the CH₃O₂, CH₃SO, CH₃SO₂, CH₃SO₃, CH₃SCH₂O, CH₃SCH₂O₂H, CH₃SCH₂O₂NO, CH₃SCH₂O₂NO₂, CH₃SCH₂O₃ and CH₃SCH₂O₄ species were determined.