Theoretical Study Of The Reaction Mechanism Between Creech's Intermediates And Several Species In The Atmosphere

Criegee intermediates?CIs?are a very active class of molecules in the atmosphere,which play a key role in controlling the atmospheric budget of hydroxyl radical,organic acids,and secondary organic aerosols.In order to better understand the reaction activity of CIs and the reaction mechanisms of CIs with atmospheric molecules,in the present study,the detailed reaction mechanisms of CIs with CH₄,N₂,N₂O,and CO₂ have been systematically investigated employing the quantum chemistry as well as the atoms in molecules theory and ab initio molecular dynamics.The main research contents are summarized as follows:Firstly,the detailed reaction mechanisms of the simplest Criegee intermediate CH₂OO and its derivatives with CH₄ have been explored at the CCSD?T?/AUG-cc-pVTZ//B3LYP/6-311++G?d,p?level of theory.Two pathways A and B have been identified for the reactions of CIs with alkanes.In pathway A,CIs can act as an oxygen donor by inserting its terminal oxygen atom into the C-H bond of CH₄,resulting in the formation of alcohol species.The corresponding energy barriers ranging from 6.5 to 24.1 kcal/mol are associated with the O-O bond strength of CIs.Meanwhile,this pathway is more favorable thermodynamically,where the free energy changes?enthalpy changes?range from-81.1?-78.3?to-110.9?-109.0?kcal/mol,respectively.In pathway B,addition reaction to produce the hydroperoxides occurs,accompanying with the hydrogen transfer from CH₄ to the terminal oxygen atom of CIs.The corresponding energy barriers ranging from 17.3 to 30.9 kcal/mol are higher than those in pathway A.Further calculations of the rate constants suggest that pathway A is the most favorable reaction channel and the rate constant exhibits a positive temperature dependence.To further validate the possibility of the reactions of CIs with other alkanes,the open-chain alkanes and cycloalkanes have been employed to react with CH₂OO.In addition,the conformation-dependent reactivity for these reactions has been observed.The present findings can enable us to better understand the potential reactivity of CIs in the presence of the alkane species.Secondly,the detailed reaction mechanisms of the CH₂OO and its derivatives with N₂ and N₂O have been investigated at the same level of theory mentioned above.It was shown that CIs can act as an oxygen donor by transferring its terminal oxygen atom to N₂,resulting in the formation of N₂O.Depending on the specific CIs,the corresponding energy barriers range from 7.67 to 26.40kcal/mol,which are associated with the O-O bond strength of CIs.The free energy changes?enthalpy changes?for this reaction range from-28.86?-27.69?to-58.61?-58.45?kcal/mol,indicating that the reactions of CIs with N₂ are favorable to occur thermodynamically.Similarly,CIs can also oxidize N₂O by transferring its terminal oxygen atom to the terminal N atom of N₂O,resulting in the formation of ONNO species followed by its decomposition to NO easily.Depending on the specific CIs,the corresponding energy barriers range from 8.79 to 28.85 kcal/mol and the free energy changes?enthalpy changes?for the whole reaction range from-8.46?-6.15?to-38.22?-36.91?kcal/mol,which are associated with the O-O bond strength of CIs.Moreover,analyses of the rate constants suggest that the reactions of CIs with N₂ and N₂O exhibit a positive temperature dependence within the available temperatures.In addition,the conformation-dependent reactivity of these reactions has been observed via the investigations of the substitution effects including halogenation and alkylation.Finally,the atmospheric implications of the results have been discussed.This study not only can enable us to better understand the potential reactivity of CIs,but also can provide new insights into the conversion of N₂ to N₂O and the alternative source of N₂O in the atmosphere.Finally,the detailed reaction mechanisms of the CH₂OO and its derivatives with CO₂ have been investigated at the CCSD?T?/AUG-cc-pVTZ//M06-2X/AUG-cc-p VTZ level of theory.Besides the addition reaction?pathway A?mentioned previously,a new alternative reaction mechanism?i.e.,pathway B?,has been observed.In pathway B,CIs act as an oxygen donor by transferring their terminal oxygen atom to the carbon atom of CO₂,resulting in the formation of CO₃ and the carbonyl compound depending on the specific CIs.From the thermodynamic viewpoint,pathway B can only occur for the CIs possessing the electro-withdrawing group.The corresponding energy barriers are slight higher by about 1.85 to 3.44 kcal/mol than those in pathway A,implying that the two pathways of the reaction involving the CIs possessing the electro-withdrawing group have a certain competitivity.On the contrary,the selected reverse reaction of pathway B is favorable kinetically and thermodynamically.Namely,CO₃ can react with the carbonyl compounds possessing the electron-releasing substitutents to produce the corresponding CIs.Two pathways C and D have been identified for the reaction of CO₃ with carbonyl compounds.In both pathways,CO₃ can act as an oxygen donor by donating its terminal oxygen atom to the carbonyl oxygen and carbon atom of carbonyl compounds,resulting in the formation of CIs and dioxiranes,respectively.Here,both pathways C and D are favorable thermodynamically and the energy barriers of pathway C are much lower by about 12.02-16.15 kcal/mol than those of pathway D.Therefore,pathway C should be the predominant reaction channel kinetically,providing an alternative approach to the production of CIs.Moreover,the conformation-dependent reactivity for these reactions has also been observed.