Quantum Chemistry Study On The Reaction Mechanism Of SO₂ And H₂O In The Formation Of Acid Rain

With development of the modern industrial technology, the air pollution question has caused more and more concerns, and the destroy caused to the ecological and living environment by the acid rain has already been one of the ten important problems threatened the world environments. In this paper, based on the context of atmospheric chemistry, the H₂SO₃ stable molecular geometries and properties have been studied by means of Density Functional Theory (DFT) methods of quantum chemistry, and we discussed the reaction mechanism of SO₂ and H₂O. Important information of potential energy surfaces such as structures and energies of intermediate isomers and transition states, possible reaction channels, reaction mechanisms and major products were obtained from the theoretical investigations. Some conclusions that were made in the present thesis may be helpful for further theoretical and experimental studies of this kind of reactions. The whole paper consists of four chapters, the main results are summarized as follows:1. By comparing the DFT/B3LYP and HF method, we thought that the DFT method is the best and used it throughout the research. The optimization configurations and frequency analysis of the possible structures of H2SO3 were calculated by using DFT/B3LYP method with 6-311++G(3df,2p) basis set, the results show that H₂SO₃ has three local minima. Accordingly, the most stable isomers were analysed with NBO by using B3LYP/6-311++G(3df,2p) method., the effect of stability of H₂SO₃ was discussed, and the relationship between forms and characteristics of H₂SO₃ was also reported.2. The reaction mechanism of SO₂ and H₂O has been studied by using quantum chemistry calculation methods. The geometries for all the stationary points on the potential energy surfaces were optimized fully, respectively, at the B3LYP/6-311++G(3df,2p) levels, four intermediates and eight transition states were obtained. All the transition states were verified by the IRC calculation and frequency analysis, and single-point energies of all the species were calculated at the QCISD/6-311++G(2df,p) level. The mechanism of reaction was confirmed and it showed six reaction channels, the channel (1) and (4) are the main reaction channels, the energy barrier is 146.73 kJ·mol^-1. at the same time, all the formation is endothermic reaction.