Theoretical Study Of Anharmonic Effect In The Combustion Of The HFCO And C₆H₆S Systems

The essence of the combustion phenomena in the combustion chamber of engine is chemical reaction.One of the main tasks of chemistry is to investigate the change of matter, and during the change process, the rate of change is a very significant factor. Nowadays, chemists have noticed that the anharmonic effect plays a significant role in dissociation of both clusters and molecular systems, especially in those with highly flexible transition states.In this thesis, the rate constants of the unimolecular decomposition reaction of H(D)FCO and thiophenol(C6H6S) radicals are calculated in canonical and microcanonical systems with the RRKM theory and the Yao-Lin(YL) method in order to investigate the anharmonic effect on the decomposition reactions. First, we use Gaussian 03 to optimize the geometries of the reactants and transition states to get the vibrational frequencies at MP2/6-311++G(3df,3dp) and MP2/6-311G(d,p) levels, respectively. Meanwhile, the single-point-energy of each geometry is optimized with CCSD(T) method, the barrier height of each reaction is obtained from zero-point-energy correction, and the total number of states, the density of state and the rate constants are calculated according to RRKM theory and YL method, then, we obtain the influent of the anharmonic effect in the combustion reaction channel.First, as to the unimoleculer reactions of H(D)FCO radical, we have calculated the harmonic and anharmonic rate constants. We find that the anharmonic effect is not significant. The harmonic and anharmonic rate constants of DFCO decomposition are lower than that of the HFCO decomposition in different conditions, because the anharmonic constants of HFCO is higher than that of DFCO, the depth of the HFCO is lower than that of the DFCO. Secondly, for the unimoleculer reaction of thiophenol radical, we have calculated the harmonic and anharmonic rate constants as well. We find that the anharmonic effect of the reaction channel A、C、D、E is not significant. The anharmonic effect of reaction channel B can not be ignored.In sum, we have three conclusions as:1、the harmonic and anharmonic rate constants increase with the increasing temperatures and total energies both in the canonical and microcanonical systems of the combustion reaction in the combustion chamber of turbine engine.2、the anharmonic effect in the combustion reaction is not significant for the both two radicals except the reaction channel B of thiophenol radical.3、the YL method works suitably for the anharmonic rate constants in the process of combustion of the unimolecular reaction both in microcanonical and canonical systems.