High-Precision Computational Study On Rate Coefficients Of Radical Hydrogen Abstraction And Hydrogen-Shift Reactions

Secondary organic aerosol is one of the important components and precursors of atmospheric pollution,which is closely related to atmospheric visibility,the generation of fine particulate matter,human health and the balance of radicals in the atmospheric environment.Exploring the chemical mechanisms and kinetics related to the formation of secondary organic aerosols can not only promote the improvement and development of relevant atmospheric and combustion models,but also help find a scientific path to harmonious coexistence between humans and nature.This paper focused on the study of the typical volatile organic compounds related to the formation of secondary organic aerosols and performed high-precision kinetics calculations for their key radical hydrogen abstraction and hydrogen-shift reactions in atmosphere and low-temperature combustion conditions.This paper also discussed the kinetics behaviors of volatile organic compounds under wide temperature and pressure conditions and various factors affecting the accuracy of rate coefficients in detail,which provide reliable data support and theoretical basis for the study of relevant atmospheric pollution mechanisms.Among the volatile organic pollutants emitted by man-made sources,this paper presented a high-precision theoretical study on the kinetics of the o-xylene reaction with OH radical,analyzed the competitive relationship between its hydrogen abstraction and addition reactions over a wide temperature and pressure range and provided detailed reaction branching ratios that are difficult to measure experimentally.We also found that compared to the toluene reaction with OH radical,the additional methyl group of o-xylene can significantly increase the pressure dependence in low-temperature combustion.This study confirms the previous experimental results and extends the scope of kinetics study to a wider range of temperature and pressure,providing direct data support for the improvement and development of atmospheric and combustion models that include o-xylene.Among the volatile organic pollutants emitted by biogenic sources,this paper conducted a high-precision theoretical study on the kinetics of the isoprene peroxy radical system.We found that due to the competition of O₂ loss channel,the phenomenological rate constants and quantum tunneling of the peroxy radical hydrogen-shift reaction both exhibit significant pressure dependence,which is helpful to understand the chemical kinetic behavior of isoprene peroxy radical under atmosphere and low-temperature combustion conditions.By solving the master equation,we directly observed a two-stage time evolution of the isoprene peroxy radical,namely the fast transformation stage and the synchronous decline stage with the bimolecular reactant.We also estimated the shortest half-lives of the isoprene peroxy radical at different temperatures,pressures,and altitudes,which provide the theoretical reference for the lifetime estimation of trace species in atmospheric studies.Finally,this paper focused on four typical peroxy radical hydrogen-shift reactions and found an inherent characteristic that cannot be ignored in this system,namely multireference character,by systematic high-precision electronic structure calculations.Based on benchmark results,we recommended a series of well-performed density functional model chemistries and co-designed a new density functional method M06-HS which specially applies to the peroxy radical hydrogen-shift reactions.In addition,the key roles of the quantum tunneling effect and multi-structural torsional anharmonicity in low-and high-temperature regions have also been analyzed in detail,respectively.