The Microscopic Dynamics Of The Atmospheric Ch <sub> 2 </ Sub> Sh + No <sub> 2 </ Sub> And Ch <sub> 3 </ Sub> The Ssch <sub> 3 </ Sub> + Oh Reaction System Research,

Organic sulfur compounds from the combustion and oxidation of sulfur-containing fules have significant impact on the environment and climatic change. For example, the acidic rain, visibility reduction and ozonosphere breakage etc. Therefore, the problem about all the transfer and oxidation of organic sulfur compounds are paid attention by many scientists. Some small molecules containing sulfur (for example, CH₃S, CH₂SH) and non-stabilization sulfide (CH₂S, CH₃SSCH₃) are the important intermediates, so the oxidation reactions of sulfide with radicels aer significant about prevention of atmospheric pollution.With development of the modern computing technique and quantum chemistry theory, computer science and quantum chemistry theory are widely applied in the field of mechanism and kinetics. Our aim of the dissertation is to provide theoretically basics to reveal the detailed mechanisms and dynamics of CH₂SH + NO₂, CH₃SSCH₃ + OH reactions. Using the Density Functional (DF) methods, the Moller-Plesset theory MPn, and the configuration interaction method (CI), the structures, the frequencies, the thermodynamic data of the reactants, products and the transition states along the reaction pathways have been obtaind as well the potential energy surface information. We further use the Polyrate 8.2 programs to calculate the rate constants by means of the canonical variational transition state theory with small curvature tunneling correction.The main contents and conclusions in our work are listed as follows:In the 3rd chapter, the mechanism for the reaction CH₂SH with NO₂ was investigated at the HL//B3LYP/6-311-H-G(2df,p) level on singlet potential energy surface. The result showed that CH₂SH + NO₂ system has four reaction channels.NO₂ attacks the C atom of CH₂SH to form an adduct HSCH₂NO₂(a), followed by C-N bond rupture along with a series of rearrangement, isomerization. The 4 products were gained finally. All the channels are exothermic reactions and the reaction energies are -150.37, -148.53, -114.42 and -131.56 kJ·mol^-1, respectively. The channel Râ†'aâ†'TSa/P1â†'P1 is the dominating channel for the reaction of CH₂SH with NO₂. The rate constants of the channel (1) Râ†'aâ†'TSa/P1â†'P1 (CH₂S + trans-HONO) are evaluated by means of the k^TST,k^CVTand k^CVT/SCT using Polyrate 8.2 procedure. The fitted three-parameter expression for the channel (Râ†'aâ†'TSa/P1â†'P1) is k^CVT/SCT=8.3×10^-40T^4.4exp(12789.3/T) cm³Â·molecule^-1·s^-1 in the temperature range of 200-3000 K.In the 4th chapter, the mechanism of isomerizazion 1,3-H shift, 1,4-H shift reactions were studied. We found 6 pathways about H shift of CH₂SH + NO₂ reaction. The results show that all the channels are exothermic reactions, but activation energies are high (238.34-258.32 kJ·mol^-1) with complicated non-primitive process. Compared with the reaction pathways for the 3rd chapter, H shift reactions are the secondary pathways in the CH₂SH + NO₂ reaction.In the 5th chapter, a theoretical study of the mechanism for the reaction of CH₃SSCH₃ with OH in gas phase was carried out. Using the MPW1PW91, B3LYP and BHandLYP methods with the 6-311++G(d,p) basis set, The geometry parameters and frequencies of stationary species were obtained. We found 5 intermediates and 6 transition states and probed various possible reaction pathways. The dominating channel is CH₃SSCH₃ + OHâ†'IM1â†'TS1â†'P1 (CH₃SH + CH₃SO). All reactions are thermodynamically favorable except for P4 (CH₃ + CH₃SSOH). The reaction energy of five reactions are -74.04, -28.42, -46.90, 28.03 and -89.47 kJ·mol^-1 at the QCISD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) level, respectively. The P1 (CH₃SH + CH₃SO) might be favored over P2 (CH₃S + CH₃SOH) considering from both energetic and entropic factors. There is a some different results compared with the experimental measurement in dominating prcduct. We hope that this work may provide helpful information on the reaction mechanism and further laboratory identification of the products.