Of Several Sulfur-containing Small Organic Molecules And Ho <sub> 2 </ Sub> Reaction Mechanism Of The Reaction Rate Constant

Dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) are the largest natural contributors to sulfur in the tropospher, and its atmospheric oxidation have been suggested to play an important role in the atmosphere and biosphere such as ozonosphere breakage, the acid rain and climate modification etc. CH3S, CH3SO, CH3SS and CH3S(S)O probably are key intermediates in the atmospheric oxidation of DMS and DMDS. So the oxidation reactions of organic-sulfur compounds with radicals are significant about prevention of atmospheric pollution, flux of interstellar species.The goal of this dissertation is to investigate the detailed mechanisms and dynamics of CH3SO+HO2, CH3SS+HO2(DO2) by using the Moller-Plesset theory(MPn), the Density Functional Theory(DFT), and the configuration interaction theory (CI). Structures, frequencies, thermodynamic data of the reactants, products and the transition states along the reaction pathways have been obtained as well the potential energy surface information. The rate constants of the domain channels are evaluated using VKLab program by means of the classical transition state theory(TST) and the canonical variational transition state theory(CVT) in which the small-curvature tunneling correction was included.The whole dissertation includes four chapters. In Chaper 1, the previous studies on CH3S, CH3SO, CH3SS, CH3S(S)O with simple atmospheric radical(X, XO, OH, HO2) in recent years were described. In Chaper 2, the wide application of Quantum Chemistry was summarized, and the background of useful and reliable quantum methods in our studies was described. In Chaper 3 and 4, the mechanisms of reactions CH3SO+HO2 and CH3SS(CF3SS)+HO2 have been discussed respectively.1. The mechanism for the biradical reaction CH3SO with HO2 was investigated at QCISD(T)//MPW1PW91/6-311G(d,p) level on singlet and triplet potential energy surfaces. The results showed that there are six possible reaction channels(seven pathways) for the CH3SO+HO2 raection system shown as following:There are three channels on the singlet potential energy surfaces, and the lowest enery barrier(61.18 kJ·mol-1) is channel(2) Râ†'1TS1â†'1P1(CH3SOH+1O2). On the triplet potential energy surfaces also have three channels. The major channel(1) Râ†'3IMâ†'P1(CH3SOH+3O2) includes two reaction pathways, which apparent activation energies are 12.01 and -30.04 kJ·mol-1 respectively, and the dominant path(2) Râ†'3IMâ†'3TS2â†'P1(CH3SOH+3O2) is a barrierless process. The rate constants of the path(2) are evaluated by means of the classical transition state theory(TST) and the canonical variational transition state theory(CVT) including the small-curvature tunneling correction. The fitted three-parameter expression for the path(2) is kCVT/SCT=4.08×10-24T3.13exp(8012.2/T) in the temperature range of 200-2500 K, in which k takes unit of cm3·molecule-1·s-1. In addition, the variational effect was almost negligible in the entire process, while the tunneling effect is considerable at the lower temperature. Channel(3) Râ†'3TS3â†'P3(CH3S(O)O+OH on the triplet potential energy surface are reported for the first time.2. The mechanisms of CH3SS+HO2 and CF3SS+HO2 systems were investigated using the same theoretical method(QCISD(T)//MPW1PW91/6-311G(d,p)). The calculated results showed thatthe mechanisms of these reactions are similar to the reaction CH3SO+HO2. The lowest energy reaction pathway occurs on the triplets PES. The dominant reaction pathway involves the direct H-atom transfer from HO2 to CH3SS(CF3SS) that leads to the products CH3SSH(CF3SSH)+3O2. For the CH3SS+HO2 system, the major channel(1) includes two pathways, in which apparent activation energies are 21.19 and 2.47 kJ·mol-1 respectively. The fitted three-parameter expression for the path(2) is kCVT/SCT=1.74×10-24T3.26exp(531.94/T) cm3·molecule-1·s-1. Channel (7) Râ†'3TS7â†'P7(CH3SSO+OH), (8) Râ†'1IM8â†'1TS8â†'P8(CH2S(S)O+H2O), and (9) Râ†'3TS9â†'P9(CH2SS+3H2O2) are reported for the first time toward the similar reaction system.The mechanism of CF3SS+HO2 is similar to that of CH3SS+HO2 reaction. However, reaction channels on the fluorine abstraction reaction were different from the hydrogen abstraction reaction due to C-F bond with much larger energy than C-H bond, only channel(6) Râ†'1FM6â†'FTS6aâ†'FP6a (CF2S+1SOO+HF) existed in CF3SS+HO2 reaction system.