Theoretical Study On The Reaction Mechanism Of C₂H₅O₂ With XO（X=Cl,Br,I） In The Atmosphere

In recent years,the destruction of atmospheric ozone layer has drawn more and more attention.Peroxide radicals and halogen monoxides XO（X=Cl,Br,I）have been playing important catalytic effects in the cycle of ozone,so the studies on the reactions of the peroxide radicals and the halogen monoxides XO（X=Cl,Br,I）have practical significance for understanding the destruction of the ozone layer.This paper taking the reaction mechanisms of C₂H₅O₂ and XO（X=Cl,Br,I）as its research object made a detailed study on the microcosmic mechanism of the three reactions with quantum chemistry methods,analyzed the products of each reaction,discussed the breaking and formation of chemical bonds at molecular level.It is expected to give further knowledge of the atmospheric chemical properties of these reactions,and provide useful theoretical data for further laboratorial investigations.This paper studied the mechanisms of the three reactions C₂H₅O₂+XO（X=Cl,Br,I）using QCISD（T）/6-311++G（2df,2p）//B3LYP/6-311++G（d,p）methods,optimized the geometric configuration of the Reactants（R）,transition states（TS）,intermediates（IM）and products（P）at the density functional of B3LYP/6-311++G（d,p）and B3LYP/6-311++G（2df,2p）level.The intrinsic reaction coordinates were calculated for each transition state to confirm the specific reactants and products to which they are attached.In order to obtain more accurate energy information,the QCISD（T）/6-311++G（2df,2p）method was used to calculate the single point energy.On this basis,the calculation results of each reaction channel are analyed in detail.The results indicate that the reactions of C₂H₅O₂+XO（X=Cl,Br,I）proceed on both singlet and triplet potential energy surfaces,and the main reaction channels proceed on the singlet potential energy surface,the reaction channels of the triplet potential energy surface is negligible due to high reaction energy barriers or unstable products.The main conclusions are summarized as follows:（1）C₂H₅O₂+BrO:4intermediates（CH₃CH₂OOOBr,CH₃CH₂OOBrO,CH₃CH₂OBrOO and CH₃CH₂BrOOO）,15 transition states,13 possible products and20 reaction channels were generated during the reaction.It is obtained that we can get two main reaction channels,and the main products are CH₃CHO+HOBrO,CH₃CHO+HBrO₂ and CH₃CH₂OOOBr,CH₃CH₂OOBrO,CH₃CH₂OBrOO after the analysis in the atmospheric standard conditions.Other products are negligible due to high energy barriers or unstable products.（2）C₂H₅O₂+IO:During the reaction,we can get 3 intermediates（CH₃CH₂OOOI,CH₃CH₂OOIO and CH₃CH₂OIOO）,12 transition states,11 possible products and 17reaction channels.After analysis,we can get four main reaction channels,and the main products are C₂H₅O+IOO,CH₃CHO+HOIO,CH₃CHO+HIO₂ and CH₃CH₂OOOI,CH₃CH₂OOIO below 300K.Other products are negligible due to high energy barrier or unstable products.（3）C₂H₅O₂+ClO:4 intermediates（CH₃CH₂OOOCl,CH₃CH₂OOClO,CH₃CH₂OClOO and CH₃CH₂ClOOO）,15 transition states,13 possible products and16 reaction channels were produced during the reaction.After analysis,there are four main reaction channels,and the main products are C₂H₅O+ClOO,CH₃CHO+HOClO,¹CH₃CHOO+HOCl,C₂H₅OCl+O₂（³Σ）and CH₃CH₂OOOCl,CH₃CH₂OOClO,CH₃CH₂OClOO under standard conditions.Other products can be ignored due to high energy barrier or unstable products.（4）Halogen Substitution Effect:From the analysis of the three reactions of C₂H₅O₂+XO（X=Cl,Br,I）,it can be seen that halogen substitution effects have little effect in such reactions,no matter the structure of the intermediates or the analysis of the reaction channels,major channels and major products.Whether it is longitudinal comparison that the relative energy order of the isomers of all the intermediates ROOOX（R=C₂H₅）in the reaction of the halogen monoxide XO（X=Cl,Br,I）with the C₂H₅O₂ from the most stable to the most unstable structure is IM3（ROXO₂）>IM1（ROOOX）>IM2（ROOXO）>IM4（RXO₃）,or horizontal comparison that the relative energyΔE of IM1,IM2,IM3 is in the order of IO<Br O<ClO and the corresponding stability is ClO<BrO<IO,IO is the most reactive,which infers that the halogen substitution effect on the RO₃X surface is meaningless.