Study On The Microscopic Mechanism Of Hydroperoxyl Radical And Typical Peroxyl Radical Conversion

In this paper,mainly based on the basic principles of quantum mechanics,the microscopic mechanism study of hydroperoxyl radical and typical peroxyl radical conversion is mainly investigated by using density functional theory（DFT）,transition state theory and traditional transition state theory combined with small curvature tunneling,the main research contents are as follows:We first investigated the hydroperoxyl radical（HO₂）reaction with hydroperoxyl radicals using the density functional theory approach M06-2X combined with the MG3S basis set as an initial conjecture and the coupled cluster theory approach CCSD（T）-F12（a）approach based on different basis groups for the optimization of the reactants,pre-reaction complexes,transition states,and products involved in the hydroperoxyl radical self-reaction.We report the hydrogen pumping kinetics of HO₂on the triple potential energy surface by using our recently developed two-level strategy that incorporates transition state theory at the benchmark test results CCSDTQ（P）/CBS//CCSD（T）-F12a/cc-p VTZ-F12 level and at the density functional theory method PWB6K/6-311+G（d,p）level using conventional transition state theory and the recrossing and tunneling effects obtained by small curvature tunneling.We find that CCSDT（Q）/CBS is a good approximation for this reaction system beyond CCSD（T）calculations,and the main contribution of the CCSDT（Q）-CCSDT component to beyond CCSD（T）calculations is-1.10 kcal/mol.We also find that the potential barrier height of PWB6K/6-311+G（d,p）is in good agreement with our best estimate.Next,the reaction of hydroperoxyl radical with methylperoxy radical（CH₃O₂）was investigated using the density functional theory approach M06-2X combined with MG3S basis set as the initial conjecture,and the structure and frequency of the compound optimized by the coupled cluster theory approach CCSD（T）-F12（a）approach based on the cc-p VDZ-F12 basis group as the benchmark,using MW3X-L/CCSD（T）-F12a/cc-p VDZ-F12 theoretical approach was used to calculate the single point energy for the reaction of hydroperoxyl radicals with methyl peroxyl radicals.We find that the enthalpy of activation of the transition state TS2A is 1.56kcal/mol higher relative to the reactants at 0 K,while the enthalpy of activation of the transition state TS2B is 2.37 kcal/mol lower relative to the reactants at 0 K.We find that the density functional theory approach M08-HX method combined with the MG3S basis set is in good agreement with our best estimate.We use the recrossing and tunneling effects obtained at the MW3X-L/CCSD（T）-F12a/cc-p VDZ-F12 level of theory using transition state theory and at the M08-HX/MG3S level using conventional transition state theory and small curvature tunneling.