Calculated rate constants of main C5 PFK (C5F10O) decomposition reactions: An environmental-friendly alternative gas in electrical equipment

Studies on candidate gases of SF6, the insulating and interrupting medium in electrical equipment, have become a hot topic in recent decades. C5-perfluorinated ketone (C5F10O) was reported as a potential replacement due to its excellent insulation capacity. However, the decomposition property of C5F10O under discharge, which is closely related to insulation deterioration mechanism, is still unknown. Although the fundamental decomposition pathways of C5F10O were reported [1], the corresponding rate constants are essential but not computed yet. Therefore, we calculated the rate constants of different decomposition reactions using transition state theory (TST) combined with density functional theory (DFT). The structural optimizations, vibrational frequency calculations and energy calculations of the species involved in reactions were carried out with DFT-(U)B3LYP/6-311G(d, p) method. Detailed potential energy surface (PES) was then investigated thoroughly by the same method. For reactions with a transition state (TS), each stationary point on PES was analyzed by a harmonic vibrational frequency analysis and characterized as a minimum (reactants or products with all real frequencies) or a TS (with only one imaginary frequency). Intrinsic reaction coordinate (IRC) calculations were used to verify each TS. Then the corresponding rate constants were estimated by conventional transition state theory (CTST). For barrierless reactions, the broken symmetry guess were added for optimization where the selected bond distance was held constant. Then the rate constants and equilibrium constants were estimated by canonical variational transition state theory (VTST). The results are hopefully to lay a theoretical basis in further evaluating and online-monitoring the insulation condition of C5F10O gas-insulated electrical equipment.