CHnF4-n与O3吸氢反应途径和速率常数计算

用量子化学方法, 从理论上探讨了CHnF4-n(n=2,3)与臭氧反应的微观机理, 并计算了各反应在不同温度下的速率常数.

Reaction Path Dynamics and Theoretical Rate Constants Calculation for CHnF4-n+O3→HOOO + CHn-1F4-n ( n = 2,3) Reactions

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 kCVT/SCT(T)=2.76×10-34T5.81 e(-13975/T) and kμVT/Eckart(T)=1.15×10-34T5.97 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 kCVT/SCT(T)=2.29×10-36T6.42 e(-15451.6/T) and kμVT/Eckart(T)=1.31×10-36T6.45 e(-15465.8/T), respectively.