Theory Studies On The Anharmonic Effect Of Several Unimolecular Reactions In The Combustion

Combustion plays an important role in daily life. At present, approximately 90 percent of the energy is generated by the combustion in our world. The application of combustion is very extensive. Almost all the power production of human needs is related to the fule combustion. In the power production of human needs, the engine is an important thermal energy power installation. The essence of the combustion of engine fuel is chemical reaction. So investigating the chemical kinetic process of combustion of fuels, it is of great significance to improve the combustion efficiency, control pollutants and research on alternative fuels. In the combustion process of the engine fuel, the fuel pyrolysis process is also very important. Investigating its chemical kinetic process, it is of great benefit to improve the quality of atomization, control air supply and the temperature of the ignition and combustion chamber. As an important parameter of chemical kinetics, the rate constant of chemical reactions is an important scientific data of combustion chemistry. Besides, the importance of the anharmonic effect in unimolecular dissociations, particularly in molecular clusters becomes more and more significant.In this thesis, the rate constant of the unimolecular dissociations of M2+(H2O)2(M=Be, Mg, Ca), CF3XCF2CH3 (X=Cl, Br) and CF3XCF2CD3 (X=C1, Br), CH3OOH and CD3OOD, CH2OHCH2OH, CH2OHCHOHCH2OH and CH3OCH3 are calculated with the Rice-Ramsperger-Kassel-Marcus (RRKM) theory and Yao-Lin (YL) method in order to investigate the anharmonic effect on the unimolecular dissociations, respectively. First, we use Gaussian 03 to optimize the geometries of the reactants and transition states of the unimolecular dissociations to get the harmonic and anharmonic vibrational frequencies at the MP2/6-311G(d,p), B3LYP /6-311++G(d,p), MP2/6-311++G(3df;3pd), MP2/6-311++G(d,p), MP2/6-311G(d,p) and MP2/6-311++G(3df,3pd) levels, respectively. Second, the single-point-energy of each geometry is optimized with CCSD(T) or CBS-QB3 method, the barrier height of each reaction is obtained from zero-point-energy correction. Last, according to RRKM theory and YL method, the total number of states, the density of state for the microcananical case and the rate constants are calculated.As the results show that:(1) With the rising of the temperature, the rate constant increases, while the growth rate of the rate constant decreases gradually. (2) As to the similar structure reactants, the greater symmetry the reactants have, the less anharmonic effect appears in the reaction. (3) In deuterated case of the reactants, the anharmonic effect of the reaction system changes. That is to say, the isotope effect for the anharmonic effect has certain effect.