Theoretical Studies On The Degradation Reactions Of Several Air Pollutants With Hydroxyl Radical

With the increasing of environmental problems in modern society, especially the human subsistence is closely related with the quality of atmospheric environment, how to control the air pollution has been caused widespread public concern. The comprehensive understanding on the mechanism and dynamics data about the degradation process of the air pollutants in the atmosphere is the most useful reference for control the air pollution. However, the differences in experimental conditions and technical levels bring about the diverse results of the same reaction system. Therefore, it’s necessary to propose a detailed theoretical research about the main degradation process of the air pollutants under the atmosphere. In this thesis, the double-level direct dynamics method has employed to study the H-abstraction reaction mechanism about morpholine(C4H9NO) and 2,2,3,3-tetrafluoropropanol(CHF2CF2CH2OH) with OH radical, respectively. And the comprehensive dynamical properties of the two reactions are investigated. Accordingly, the main contents are as follows,C4H9NO+OH→productsCHF2CF2CH2OH+OH→productsThe electronic structure calculations are carried out by the Gaussian 09 program. The geometries and frequencies of all the stationary points including the reactants, transition states, products, and complexes are performed by using the M06-2X or BB1K method. The minimum energy path(MEP) is calculated by the intrinsic reaction coordinate theory(IRC), the single-point energies for the stationary points and a few extra points along the MEP are computed by the MC-QCISD/3 method. By means of the Polyrate 9.7 program, the rate constants are calculated by the improved canonical variational transition states theory, and the small-curvature tunneling correction has been considered.The main results of this thesis are summarized as follows,(1) A dual-level direct dynamic study has been employed to investigate the H-abstraction reaction of C4H9NO with OH radical at MC-QCISD/3//M06-2X/6-311+G(d, p) levels. The CVT/SCT rate constants are estimated over a wide temperature range from 200 to 1000 K, and the negative temperature dependence of rate constant is found below 500 K. The H-abstraction from the axial hydrogen of the-CH2 group (C attached to N) is the predominant channel at low temperature, and the H-abstraction from the axial hydrogen of the-CH2 group (C attached to O) and that from the-NH group are located in the second and third place. As the temperature increases, the H-abstraction from the-NH group becomes more competitive and then turns into the important channel for the title reaction as temperature exceeds 500 K. The contribution that the H-abstraction from the equatorial hydrogen atoms of the-CH2 group (C linked to N or O) to the overall reaction can be almost neglected over the temperature range of 200-1000K. The calculated rate constants are in good accordance with experimental values.(2) The theoretical investigation on the reaction CHF2CF2CH2OH+OH is studied by the dual-level direct dynamic method, the ICVT/SCT rate constants are calculated over a wide temperature range from 200 to 2000 K at MC-QCISD/3//BBlK/6-31+G(d, p) levels. For reactant CHF2CF2CH2OH, the lowest energy conformer with C1 symmetry(denoted as conformer Ⅰ) and another conformer with C. symmetry(denoted as conformer Ⅱ), are located by the rotations of the-OH,-CHF2,-CH2 groups, the relative population of the two conformers are considered in the overall rate constants. The calculation result suggests that conformer I dominates the above reaction over the whole temperature range. Finally, the three-parameter fits based on the ICVT/SCT rate constants for the title reactions within 200-1000 K is given, and the theoretical results are in good accordance with experimental values.In conclusion, we employ the dual-level direct dynamics method to study the accurate reaction profile and obtain the rate constants of the above reactions, and we hope that the theoretical results may be useful for providing a theoretical basis and reference for the further experimental study.