Figure 8 Potential energy diagram of the reactions between R125 and H·, OH·.
In order to further explore the fire extinguishing mechanism of R123, the reactions of R125 with H· and OH· radicals are also calculated as a comparison (Figure 8). The same as R123, R125 and free radicals mainly undergo substitution reactions and abstraction reactions. For the reaction of R125 with H·, three additive reaction paths are theoretically exhibited, with P17 (path 17), P18 (path 18) and P19 (path 19) separately generated via TSd1, TSd2 and TSd3 by consuming 164.9, 148.6 and 59.8 kj·mol-1. And two substitution reactions occur about R125 with OH·, which consumes 304.0 and 296.6 kj·mol-1 respectively, these reactions can generate more F· atoms. However, the product of R123 contains not only F· atoms but also Cl· atoms, Cl· atoms are easier to generate than F· and CF3· atoms, and the energy barriers that need to be overcome are lower, so the fire extinguishing performance of R123 is better. The introduction of fluorine-species reactions and chlorine-species reactions in literature, it is indicated that fluorine-species reactions have less sensitive to the burning velocity. For the chlorine-species reactions, the burning velocity is sensitive to three reactions of the initial break-down of R123, such as CF3CH2Cl=CF3+CH2Cl, CF3CHCl2+H= CF3CHCl+HCl[18]. And two of the reactions in the catalytic radical recombination cycles (HCl + OH = Cl + H2O, and Cl + HCO = CO + HCl) are affecting the burning velocity[36, 37]. In general, the chlorine-species reactions have more obvious inhibitory effect on the burning velocity.