The Investigations On Kinetics Of The Unimolecular Reactions Of Criegee Intermediates With Vinyl Group Involved

The strongly correlated system is a difficult and hot research object in the field of condensed matter physics.Criegee intermediates（R₁R₂COO）is a strongly correlated molecular systems that plays a significant role in the transformation of complex molecules in the atmosphere.However,the electronic structure of Criegee intermediates is complex and becomes more complicated as the number of carbon atoms increases,resulting in more conformers,leading to unknown reaction kinetics.In addition,vinyl-substituted Criegee intermediates are subject to internal rotation,and the commonly used coupled cluster theory single,double and perturbation triple excitation（CCSD（T））methods cannot obtain quantitative reaction kinetics for these complex systems.In this paper,we applied the fundamental principles of quantum mechanics and statistical physics to investigate the unimolecular transformation kinetics of three Criegee intermediates,acrolein oxide,methyl vinyl ketone oxide and methacrolein oxide,using density functional theory,coupled cluster theory,canonical variational transition state theory with small-curvature tunneling correction,system-specific quantum Rice-Ramsperger-Kassel theory,and master equation solution methods.The results of single-point energy calculations show that the unimolecular transformation of acrolein oxide Criegee intermediates,coupled cluster theory single,double,and perturbative triple excitation CCSD（T）methods are not sufficient to obtain quantitative potential energy surface information,and must include coupled cluster theory single,double,triple,and connected to perturbative quadruple excitation CCSDT（Q）calculations to obtain quantitative potential energy surface information.The results of CCSDT（Q）calculation were used as a benchmark reference to verify that the density functional methods MN15-L/MG3S and M06-2X/MG3S can achieve the accuracy of CCSD（T）/CBS calculation.The calculation of the zero-point vibrational energy（ZPE）of the Criegee intermediate reaction system is a challenge.The calculation results show that the changes in CCSD（T）zero-point vibrational energy in proceeding from reactant to transition states or reactant to products as calculated with various basis sets,differ from one another by up to 0.36 kcal/mol.The zero-point vibrational energy is a vital parameter in this type of reaction system,which determines whether the rotational isomerization of acrolein oxide Criegee intermediate is endothermic or exothermic process.The kinetics of the unimolecular reactions of three Criegee intermediates were studied using the above theoretical approach.The calculation results show that their unimolecular reactions are significantly affected by pressure,and in particular,the rotational isomerization pathway reduces the effective unimolecular reaction rate constant of the cyclization pathway by a factor of about three.The large falloff effect of the rate constants due to the rotational isomerization pathway is important for the analysis of reaction mechanisms containing competing rotational pathways.While it was previously thought that the rotation of conformers only affects the coordination function of the molecule and thus the reaction kinetics,this study reveals that the rotation pathway of conformers competes with other pathways and affects the reaction kinetics.