Anharmonic Effect Of The Unimolecular Reactions Of The CX₃COOX（X=H, D） Radicals And The Single-tube Ignition Test

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 constant of the unimolecular decomposition reaction of CX3COOX(X=H, D) radicals are calculated with the Yao-Lin(YL) method in order to investigate the anharmonic effect on the decomposition reactions. In this unimolecular systems, we use Gaussian 03 to optimize the geometries of the reactants and transition states to get the vibrational frequencies at different levels. 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.First, the rate constant of this reaction is calculated and it shows that the anharmonic effect is very significant. The results show that the anharmonic effect on the unimolecular dissociation of the trans-acetic acid radical is the smallest one. When the temperature is 1000 K, the harmonic rate constant (0.43×10-2 s-1) is 17.3% lower than the harmonic rate constant (0.52 X 10-2 s-1); When total energy is 25108.55 cm-1, the harmonic rate constant is 3.1% lower than the anharmonic rate constant. Second, the reactants have been deuterated out three times and the rate constant of the deuterated result is also calculated and the anharmonic effect has been discussed too. From the above results, compared with the non-deuterated results, the rate constant of the deuterated results is smaller; Both the anharmonic effect and the isotopic effect in the microcanonical system are obvious; the gap of the rate constant between the non-deuterated result and the result of deuterated out on all the hydrogens is the most obvious.The single-tube ignition test has two parts:the one is temperature of the ignition test, the other one is the spectrum of flame. The first part can give the relationship between the temperature of the ignition and the air velocity. The second part can contribute to research the ignition delay and reaction mechanism.