Several Amine Small Molecule Ionization Energy Of Ch <sub> 3 </ Sub> Nh <sub> 2 </ Sub> With Oh Reaction Mechanism Theory

Radicals and ions are the important part of the interstellar chemistry and also the instantaneousintermediate in chemical reaction process. Thermodynamics properties such as the adiabaticionization energy (AIE) etc of these species have reference value for the comprehension andprediction of chemical reaction. Moreover, intermolecular reaction between these interstellarmolecular has certain instruction value for understanding the formation of the interstellar materials.Therefore, in this thesis the theoretical researches on the AIEs of NH₃ and part of its derivates aswell as the chemical reaction mechanism between CH₃NH₂ and OH were done. The contents of thethesis consist of the following two parts:1. The theoretical calculations of the adiabatic ionization energies (AIEs) of NH₃,CHNH,CH₂NH,CH₂NH₂,CH₃NH have been carried out using the B1B95> O3LYP,OLYP,PBE1PBE,B3LYP,BB1K,MPW1K,MPWB1K and MPW1B95 methods with the 6-311+G(d,p),6-311++G(2d,2p), 6-311++G(2df,2p), 6-311G(3df,3pd) and 6-311++G(3df,3pd) basis sets.2. A theoretical study on the mechanism and the kinetics for the hydrogen abstraction reactionof CH₃NH₂ by OH radical has been presented at the CCSD(T)/6-311++G(2d,2p)//CCSD/6-31G(d)level of theory by the direct dynamics method.As considered above, the main results are given:(1) For AIEs of selected species, (a) the geometries and harmonic vibrational frequencies havehardly changed with the increasing of basis set at the same DFT method, which means the optimizedgeometries have not dramatically affected. Thus, we proposed the selective methods are suitable forcalculating geometries for the amines containing nitrogen, (b) the accuracies of the AIEs wasobviously improved by the zero-point energy correction and increasing diffuse functions. Thecalculated AIEs by the MPWlB95/6-311++G(3df,3pd) method accords much better with theexperimental values than the other methods. By the present study we expect that theMPWlB95/6-311++G(3df,3pd) method can be extended to calculate the AIE of the class of amines.(2) For the reaction of CH₃NH₂ with OH radical, (a) There are two channels for the studiedreactions, which have a stepwise mechanism: reactants→post-reactant complex→transition state→pre-product complex→products. One is the hydrogen abstraction channel from the amine groups.Another is the hydrogen abstraction from the methyl groups. The calculated standard reactionenthalpies for the above two channels are -76.50 and -98.48 kJ mol～(-1) and barrier heights are 25.25and 0.36 kJ mol(-1), respectively. The dominant product channel is to form CH₂NH₂ and H₂O via hydrogen abstraction from the CH₃ group of CH₃NH₂ by OH. (b) The rate constants are evaluated bymeans of the improved canonical variational transition state theory with small-curvature tunnelingcorrection (ICVT/SCT) in the temperature range of 299-3000 K. The calculated results show that therate constants at the experimentally measured temperatures are in good agreement with theexperimental values. Moreover, the results indicate that the tunneling effect is considerable in thelower temperatures, while the variational effect is obvious over the entire process.