DFT Theory Study Of C_mH_n Cation With N Phase Reactions

Nitrogen chemistry is very important in the synthesis of interstellar molecules. Recently,the study of the ion-molecular reactions of nitrogen atom with hydrocarbon ions is relevant interrestrial ionospheric chemistry, as well as in understanding the chemistry of extraterrestrialatmospheres (for example, nitrogen is the major component of Titan,s atmosphere). In addition,two studies explored the possibility that ion-N atom chemistry might provide important steps ininterstellar cloud synthesis. Several reaction schemes have been proposed for the interstellarsynthesis of cyanopolyacetylenes and related compounds. In this thesis, quantum chemical investigations on the potential energy surfaces of nitrogenand some cations reactions related to C_mH⁺_n, including the C₃H⁺ +N and C₂H⁺₂ +N reactions,9that are important in interstellar and combustion chemistries have been carried out. Importantinformation of potential energy surfaces such as structures and stability of intermediate isomers,possible reaction channels and reaction mechanisms are obtained from these theoreticalinvestigations. The results presented in this thesis may be very helpful for understanding thenitrogen with some hydrocarbon ions reactions in interstellar and combustion chemistries, andmay provide some elemental theoretical basis for further experiments on radical reactions. Themain results are follows: 1. The mechanism of the C₃H⁺ +N reaction in gas phase has been studied atQCISD(T)/6-311++G^**//UB3LYP/6-311G^* level by using density functional theory. Thepossible channel leading to the lowest-lying product P₂C₃N⁺+H and the potential energy surfaceshave been obtained. The results showed that the whole reaction comes through many courses,including 6 intermediates and 11 transition states, and P₁CNC⁺₂ +H is lower product. Among thereaction paths proposed, channel 1:R→IM1→TS1→IM3→TS2→IM4→TS3→IM5→TS11→P is the probable path. 2. The mechanism of the C₂H⁺₂ +N reaction in gas phase has been studied atQCISD(T)/6-311++G^**//UB3LYP/6-311G^* level by using density functional theory. Thepossible channel leading to the lowest-lying product P₃HCCN⁺+H and the potential energysurface have obtained. The results showed that the whole reaction comes through many courses,and P₂C₂N⁺+H₂ is lower product. Among the reaction paths proposed, channel d:R→IM1→TS3→IM3→TS7→ P2 is the probable path.