Theoretical Investigations On The Mechanisms For Several Important Molecule Reactions

Reactions of small radicals with neutral molecules play a significant role in diverse environments such as industrial applications, combustion flames, catalytical reactions,the interstellar medium (ISM), and so on. As a result, quantum chemical investigations on the potential energy surfaces of several important molecule reactions have been carried out in this thesis. These reactions include F + HONO, the Propene Hydrogenation Catalyzed by Metal Ir4 Cluster. 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 are obtained from the theoretical investigations. Some conclusions that are made in the present thesis may be helpful for further theoretical and experimental studies of this kind of reactions. The main results are summarized as follows:1. The reaction of F(2P) with nitrous acid has been studied theoretically using ab initio quantum chemistry methods and transition state theory. The potential energy surface was calculated at the CCSD(T)/cc-pVTZ and QCISD(T)/cc-pVTZ (single-point) levels using the UMP2/6-311++G(d,p) optimized structures. Various possible reaction pathways including the direct H-abstraction reaction and three kinds of addition reactions are considered. Among them, the most feasible pathway should be the F atom abstracting hydrogen of cis-HONO directly, leading to the products P1 HF + NO2. The other reaction pathways are less competitive due to thermodynamical or kinetic factors. Furthermore, our calculation results show that, in terms of potential energy surface, the title reaction involves all the main features of H + HONO reaction. However, the mechanisms of F with HONO are more complicated than those of H + HONO. The reaction heats of formation calculated are in good agreement with that obtained experimentally. It will provide useful information for understanding the mechanism of F atom reaction.2. Using density functional theory (DFT), the reaction mechanism of propene hydrogenated catalyzed by metalline Ir4 cluster were explored in detail theoretically. At B3LYP level of theory, the geometries of stationary points (reactions, intermediate isomers, transition states and product) were optimized and the ground state potential energy surface was ploted. The calculated results suggested that for the propene hydrogenation catalyzed by metal Ir4 cluster, the reaction may follow three reaction channels, which is c, d and e. In the major reaction channel c, the H-atom at Ir1 site first transforms to intermediate isomer 1 after surmounting TSR-1, followed by the addition of H-atom to the side C of propene, which leading to the forming of intermediate isomer 3. After that, the H-atom at Ir2 site can addition to the middle C, passing through transition state TS3-5, intermediate isomer 5 and transition state TS5-P respectively. Channel c is the most feasible reaction channel on the PES on both kinetic and thermodynamic considerations. As the highest transition states in channel d and e are a little higher than that of in channel c, they are less competitive and belong to minor channels.