Theoretical Studies on Dielectric Breakdown Strength Increasing Mechanism of SF6 and Its Potential Alternative Gases

A theoretical investigation on the dielectric insulation mechanism of sulfur hexafluoride（SF6） and its potential alternative gases at the atomic and molecular levels was made. The electronic structures of the molecules of them were calculated at the B3LYP/6-31 11＋G（d,p） level. The HOMO-LUMO energy gaps, ionization potentials, electron affinities, and dipole moments of the studied molecules at the ground state were obtained. The 11 isomerization reactions, with the harmonic vibration frequencies of the equilibrium geometries and the minimum energy path by the intrinsic reaction coordinate theory, were also obtained at the same level. The results show that the insulation gas, with the larger HOMO-LUMO energy gap, the higher ionization potential and the stronger electron affinity, can increase the dielectric breakdown strength efficiently, which is in good agreement with the available experimental finding. We suggested that the molecule with isomerization reaction occurring can dissipate the energy of hot electrons availably, which is favorable to the dielectric breakdown strength increasing for the SF6 potential alternative gas.