Theoretical Investigations On The Reactions Of XCO(X=CH₂,S) With CH(X²Ⅱ) Radical

CH radical is an important intermediate product playing important roles in various fields, such as combustion chemistry, atmospheric chemistry and environmental protection. Due to the short lives of the radicals and the difficulty to obtain the pure species, the experimental research for their structures and reaction features (especially the reaction mechanisms and the dynamics) is very difficult. Therefore, more and more attentions have been focused on their theoretical researches.With the quantum chemistry calculation methods, we studied the reactions of CH (X²Î ) with ketene (CH₂CO) and SCO molecules. The reaction mechanisms are theoretically investigated in detail. Our calculations provide the elementary theoretical evidence for further experimental research. The main results in this thesis can be summarized as follows:1. The mechanism for the CH₂CO + CH (X²Î ) reaction is investigated at the QCISD(T)/6-311+G^**//B3LYP/6-311G^** level.The computational results show that the reaction proceeds via three possible mechanisms, i.e., olefinic carbon addition-elimination, carbon-carbon double bond insertion and side oxygen addition-elimination mechanisms. Four products,P1(C₂H₃ +CO),P2(C₂H₂ + HCO),P3 (CH₂C + HCO), P4 (C₂H₂ + CO + H) are generated. As a result,P1 may be thermodynamically main product for title reaction. P4 is the final products when secondary dissociation procedure is considered. Except for the carbon-carbon double bond insertion mechanism, we also discover the other two mechanisms: olefinic carbon addition-elimination mechanism and side oxygen addition-elimination mechanism. However, direct abstraction of hydrogen atom from CH₂CO to form HCCO and CH₂ was little competitive because this channel is endothermic.2. A detailed theoretical survey on the potential energy surface for the CH (X²Î ) + SCO reaction is carried out at the CCSD(T)/6-311+G^**//B3LYP/6-311+G^** level. Depending on the site for the CH-attack on the SCO molecule, the reaction proceeds in four mechanisms, i.e., The reaction proceeds through four possible mechanism, i.e. oxygen addition-elimination mechanism, sulfer addition-elimination mechanism, carbon-sulfer bond insertion mechanism and carbon-oxygen bond insertion mechanism. Oxygen addition-elimination and carbon-oxygen bond insertion channels are unfavorable kinetically. With the lowest energy, carbon-sulfer bond insertion channel to yield P2 (HCS + CO) is most important among all the channels. Furthermore, the two channels generating P2 via sulfer addition-elimination mechanism are considerably competitive.