关键词: 臭氧, 氟代甲烷, 速率常数, 密度泛函理论

Abstract: The hydrogen abstraction reactions by ozone from fluoromethanes(CH₃F, CH₂F₂) are the most suitable processes for modeling and testing methodologies that could be applied to larger molecules or to the complete reaction kinetic schemes for the degradation of HFCs. We presented a theoretical study of the hydrogen abstraction reactions from CH₃F and CH₂F₂ by ozone molecule. The geometries, harmonic vibrational frequencies of all stationary points were calculated at MPW1K level of the theory. The energies of all the stationary points were refined by using higher-level(denoted as HL) energy calculations. The minimum energy paths(MEPs) were obtained by the MPW1K/6-31+G(d,p) level. Energetic information of the points along the MEPs is further refined by HL method. The rate constants were evaluated on the basis of the MEPs from the HL level of theory in the temperature range of 200—2500 K with the conventional transition state theory(TST), the canonical variational transition state theory(CVT) and the microcanonical variational transition state theory(μVT) based on the ab initio calculations. A general agreement was found among the TST, CVT, and μVT theories. The fitted three-parameter Arrhenius expressions of the calculated forward CVT/SCT, and μVT/Eckart rate constants of the ozonolysis of fluoromethane are k^CVT/SCT(T)=2.76×10^-34T^5.81 e^(-13975/T) and k^μVT/Eckart(T)=1.15×10^-34T^5.97 e^(-14530.7/T), respectively. The fitted three-parameter Arrhenius expressions of the calculated forward CVT/SCT, and μVT/Eckart rate constants of the ozonolysis of difluoromethane are k^CVT/SCT(T)=2.29×10^-36T^6.42 e^(-15451.6/T) and k^μVT/Eckart(T)=1.31×10^-36T^6.45 e^(-15465.8/T), respectively.

Key words: Ozone, Fluoromethane, Rate constant, Density function theory(DFT)