| The alkoxy radicals, which play an important role in the atmospheric chemistry, have great influence on the quality of atmospheric environment and human health. Among them is the ethoxy radical (CH3CH2O), which is predominantly formed and emitted to the troposphere by the atmospheric oxidation of ethanol. CH3CH2O is one of the most reactive contaminants in the atmosphere and easy to react with other active species. In addition, it is known to be involved in many atmospheric oxidation processes as a possible key intermediate. So the in-deep knowledge about reactions of CH3CH2O with other species are crucial in understanding the formation (and elimination) of oxygen-containing organics in atmosphere, which will eventually make contribution to the pollution control. The purpose of this paper is to investigate the detailed mechanisms and kinetics of the CH3CH2O+HCHO and CH3CH2O+OH reactions using the density functional theory (DFT).In chapter1, the origin of the ethoxy radical, and its important role in atmospheric chemistry, as well as the impact on atmospheric environment, are briefly introduced. The research progress of the important CH3CH2O-involved reactions are also reviewed. In chapter2, a brief introduction of the theory in quantum chemistry and computational methods, especially the ones used in the current investigations, are given. In chapter3, the results of mechanistic and kinetic study for reaction of CH3CH2O with HCHO radicals are presented. The rate constants of the dominant channel for the CH3CH2O+HCHO radical-radical reaction were computed. Meanwhile, the enthalpies of formation of several new compounds (CH3CH2OCHOH, CH3CHOCH2OH and CH2CH2OCH2OH) that have not been experimentally measured were calculated by using the key reaction principle. In chapter4, the CH3CH2O+OH reaction system, in both the singlet and triplet state, are presented. The representive processes, including the hydrogen abstraction reactions, nucleophilic reaction and addition-elimination reaction mechanism are given, along with the computed rate constants for the main channel.The main results and conclusions are summarized as follows:(1) The reaction of CH3CH2O radical with HCHO was calculated at the CCSD(T)/cc-pVDZ//B3LYP/6-311++G(d,p) level of theory. Five hydrogen abstraction channels and three H-isomerization channels were found for the title reaction. Among them,[Râ†'IMa(CH3CH2O…CH2O)â†'TS1â†'IM1bâ†'P1(CH3CH2OH+CHO)] is the most favorable channel, with an apparent activation energy of14.65kJ·mol-1. The rate constants of path R1were evaluated over a temperature range of275～1000K.The fitted three-parameter expression for path R1is kCVT/SCT=2.26×10-17T0.57exp (-1004/T) cm3-molecule-1·s-1and thus indicate that R1has a positive temperature effect over a temperature range of275～1000K. Using the key reaction, we obtained the enthalpies of formation for several new compounds (CH3CH2OCHOH, CH3CHOCH2OH, CH2CH2OCH2OH, with values of-163.8kJ·mol-1,-142.8kJ·mol-1,-234.4kJ·mol-1, respectively).(2) In chapter4, the reaction of CH3CH2O radical with OH was inversitigated at the CCSD(T)/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) level of theory, on both the singlet and triplet potential energy surfaces. Nine hydrogen abstraction channels, two substitution mechanism as well as four addition-elimination process are found for the title reaction. From the view point of energy, the channel [R10(Râ†'3TS10â†'P4(3CH3CHO+H2O)] is the dominant channel of the reaction CH3CH2O+OH. The fitted three-parameter expression for the R10is:kCVT/SCT=4.83×10-21T2061exp (428/T)cm3·molecule-1·s-1and thus indicate that R10has a moderately positive temperature effect over a temperature range of275～1000K the process for the reaction of CH3CH2O+OH on the triplet PESWe hope that our research results will be helpful in understanding the formation of oxygen-containing organic compounds in atmosphere and provide valuable information for further experimental and theoretical studies. |
PDF Full Text Request