Theoretical study on decomposition pathways and reaction rate constants of C₄F₇N with O atom

C₄F₇N is one of the promising candidates to replace SF₆ as insulating medium in power equipment. Meanwhile, the effect of an O atom on C₄F₇N decomposition is still unclear but it greatly influences the decomposition mechanism and insulating properties of C₄F₇N. In this paper, the B3LYP method, in conjunction with 6-311G(d,p) basis set, is used to study the decomposition mechanism of C₄F₇N with an O atom. The molecular structures of reactants, products and transition states (TS) in the C₄F₇N decomposition pathway, which consists of 25 reactions, are optimized. The potential energy surface of each reaction and the vibrational frequencies of each molecule or TS are studied with same method as the prerequisite for rate constant calculations using transition state theory. The results show that the CN bond breaks with the highest energy of 321.91 kcal mol^-1, so reaction (R21) (C₄F₇NO → C₄F₇O + N) plays a less important role than (R2) (C₄F₇NO → C₃F₄NO + CF₃), (R5) (C₄F₇NO → C₃F₇O + CN), (R11) (C₄F₇NO → TS1 → C₃F₅N + CF₂O) and (R15) (C₄F₇NO → TS2 → C₃F₃NO + CF₄) in the decomposition of C₄F₇NO. CF₂O and CF₄, characteristic decomposition products of C₄F₇N + O which have negative impacts on the insulating gas, are generated in reactions (R11) and (R15) with a higher rate constant at 1500 K above, respectively. CF₃ and F₃C-O are important in C₄F₇N with O decomposition because of the high overall-generation rate constants. This work is expected to provide a theoretical basis to evaluate the insulation performance of C₄F₇N-insulated power equipment and develop novel gas sensors for insulating condition monitoring.