Study On The Microscopic Mechanism Of CH₂OO Intermediates And Peroxides

The reaction mechanism and kinetics of Criegee intermediates are a hot and difficult issue in condensed matter physics research,as they provide important parameters for processes such as free radical generation,secondary organic aerosol formation,and atmospheric oxidation ability.However,due to the complex electronic structure system of the Crisegee intermediate with the characteristics of double free radicals and positive and negative ions,and also widely involved in the single molecule and bimolecular reactions in the atmosphere,it is a great challenge to study the reaction mechanism and reaction kinetics of the Crisegee intermediate.Based on quantum mechanics and statistical physics,the reaction mechanism and kinetics of the reaction between CH₂OO intermediate and atmospheric peroxides XOOH（X=H,CH₃）were studied theoretically by using density functional theory,coupled cluster theory,traditional transition state theory and canonical variational transition state theory with small curvature tunneling correction and variational correction.The reaction mechanism of CH₂OO+CH₃OOH reaction produces oxides of methyl hydroperoxyl methane and ether,respectively.The formation of dihydroperoxy methane is advantageous because the best evaluated activation enthalpy for the formation of dihydroperoxy methane at 0 K is 1.78 and 0.03 kcal mol^-1 lower than the oxide mechanism for the formation of alcohol.In the calculation of single point energy,it is shown that DF-CCSD（T）-F12b/jun’-cc-p VDZ can be used to obtain reliable geometric optimization and frequency calculations,as well as quantitative activation enthalpy of CH₂OO+H₂O₂ reaction at 0 K.In addition,it is proved that post-CCSD（T）calculation is necessary to obtain quantitative potential energy surface information for the reaction of CH₂OO intermediates with atmospheric peroxides.The total rate constant of the CH₂OO+H₂O₂ reaction has a negative correlation with temperature.Between 200 and 350 K,the reaction rate constant of CH₂OO+H₂O₂varies from 1.31×10^-13 to 3.80×10^-14 cm³molecule^-1 s^-1。The mechanism of dihydroperoxy methane formation is the main reaction channel because it has a rate constant branching ratio of up to 90%.Although the CH₂OO+H₂O₂reaction does not compete well with the H₂O₂+OH reaction,under certain atmospheric conditions,the CH₂OO+H₂O₂ reaction can have an effect on the distribution of H₂O₂.The mechanism of the CH₂OO+CH₃OOH reaction produces the oxides of methyl hydroperoxyl methane and ether,respectively.At 0 K,the activation enthalpy of the oxidation mechanism of ether is 1.11 and 3.74 kcal mol^-1 lower than that of methyl hydroperoxyl methane.Therefore,the oxidation mechanism of ether is more advantageous than that of methyl hydroperoxyl methane.It is shown in the single-point energy calculations that DF-CCSD（T）-F12b/jun-cc-p VDZ is necessary for geometry optimization,frequency calculations,and to obtain quantitative activation enthalpies for the Criegee reaction at 0 K.It is also shown again that post-CCSD（T）calculations are necessary to obtain quantitative potential energy surface information for the reaction of CH₂OO intermediates with atmospheric peroxides.The total rate constant of CH₂OO+CH₃OOH reaction decreased from 1.54×10^-11 cm³ molecule^-1s^-1 to 1.29×10^-13 cm³ molecule^-1s^-1 in the temperature range of200 and 350 K,which indicated that CH₂OO+CH₃OOH reaction had a negative temperature dependence.The rate constant branching ratio of the oxide mechanism of ether formation is up to 96%,which is the main reaction channel of CH₂OO+CH₃OOH.Under atmospheric conditions,the CH₂OO+CH₃OOH reaction can compete well with the H₂O₂+OH reaction.Therefore,the CH₂OO+CH₃OOH reaction contributes to the removal of CH₃OOH,and this reaction may be a new sink for CH₃OOH.