The First-principle Study On The Evolution Of CH₃O In The Atmosphere

In this paper,the first principle and the density functional theory?DFT?methods are used to study on the evolution of CH₃O in the atmosphere.The mainly studied in the following two aspects:We have investigated the hydrogen atom transfer processes of CH₃O to CH₂OH without catalyst and with water,ammonia,and hydrofluoric acid as catalysts using ab initio methods,density functional theory?DFT?methods,and canonical variational transition state theory with small curvature tunneling?CVT/SCT?.Herein,we have performed the benchmark barrier heights of the title reactions using W3X-L//CCSD?T?-F12a/VDZ-F12 methods.We have also performed the calculations of the combination of MPW-type,PBE-type exchange,M05-type,M06-type functional,and composite theoretical model chemistry methods such as CBS-QB3and G4.We found that the M05-2X/aug-cc-pVTZ,mPW2PLYP/MG3S,M05-2X/aug-cc-pVTZ,and M06-2X/MG3S methods are performed better in different functionals with the unsigned errors?UEs?of 0.34,0.02,0.05,and 0.75 kcal/mol for its unimolecular reaction and reactions with H₂O,NH₃,and HF,respectively.The calculated results show that NH₃ exerts the strongest catalytic role in the isomerization reaction of CH₃O to CH₂OH,comparing with H₂O and HF.In addition,the calculated rate constants show that the effect of tunneling increases the rate constant of the unimolecular reaction of CH₃O by 10²-10¹² times in the temperature range of 210-350 K.Moreover,the variational effects of the transition state are obvious in CH₃O+NH₃.The calculated results also show that the direct unimolecular reaction of CH₃O to CH₂OH is dominant in the sink of CH₃O,comparing with the CH₃O+H₂SO₄,CH₃O+HCOOH,CH₃O+H₂O,CH₃O+NH₃,and CH₃O+HF reactions in the atmosphere.The catalyst can not only affect the barrier height,but also affect the tunneling effect and variational effect of the transition state.In this work,we investigated the hydrogen atom transfer processes of CH₃O to CH₂OH catalyzed by water dimer,and CH₃O with O₂,NO reactions using ab initio methods and density functional theory?DFT?methods.The calculated results by B2PLYP/ma-TZVP indicated that the barrier height of the reaction is 7.71 kcal/mol.Through the theoretical calculation study found that CH₃O with 2H₂O reaction reduce the energy barrier of CH₃O to CH₂OH unimolecular isomerization reaction catalyzed by 2H₂O.The best functional response of CH₃O with NO reaction is B98/aug-cc-pVTZ,and the barrier is 1.56 kcal/mol.In the reaction of CH₃O and O_2,we found the calculation method closest to the experimental results is M-W3.2//CCSD?T?-F12a/VTZ-F12,the barrier was 2.22 kcal/mol,and the best functional in the test methods was M11-L/aug-cc-pVTZ,and the barrier was 2.57kcal/mol.The reaction of CH₃O with NO and O₂ is the hydrogen abstraction reaction.