Theoretical study of the neutral decomposition of SF6 in the presence of H2O and O2 in discharges in power equipment

In the presence of H2O and O-2, the dissociation products of SF6 will decompose to form several main stable byproducts (i.e. SOF2, SOF4 and SO2F2) in an electrical discharge. These byproducts are chemically active and have been shown experimentally to be associated with discharge faults. However, the relationships between the discharges and types of decomposition components are still not clear, mainly due to the fact that the complex chemical processes during SF6 discharges are not fully understood. In order to comprehensively investigate the decomposition of SF6, an approach combining density functional theory (DFT) and transition state theory (TST) was used to study the pathways of SF6 decomposition in mixtures with H2O and O-2 that involve electrically-neutral species. The complex chemical reactions were analyzed, and the corresponding rate constants were predicted. The structural optimizations, vibrational frequency calculations and zero- point energy calculations of the species involved in each chemical reaction considered were carried out using the DFT-B3LYP method. Single-point energies were calculated using the CCSD(T) method. Based on the energy information obtained, the rate constants were predicted by TST, over a large temperature range, from 300 to 12 000 K.