Electron attachment to perfluorocarbon compounds. II. c-C5F8, c-C6F10, c-C6F12, C7F8, and C8F16: Relevance to gaseous dielectrics

Abstract

Electron attachment rates αw as a function of the pressure‐reduced electric field have been measured for c‐C₅F₈ (perfluorocyclopentene), c‐C₆F₁₀ (perfluorocyclohexene), c‐C₆F₁₂ (perfluoro‐1,2,‐dimethylcyclobutane), C₇F₈ (perfluorotoluene), and C₈F₁₆ (perfluoro‐1,3‐dimethylcyclohexane). The thermal values (αw)_ther of the attachment rate for these compounds are 12.8, 12.9, 5.0, 9.2, and 2.4×10⁹ sec⁻¹ Torr⁻¹, respectively. The electron attachment cross sections σ_a(ε) as functions of the electron energy ε have been determined using the swarm‐unfolding technique; they show distinct structure at εw; (iii) the presence of multiple bonds in the molecule dramatically increases the magnitude of αw for the saturated open‐chain PFCs, but it has only a small effect for cyclic PFCs; (iv) the cyclic nature of the PFCs seems to increase greatly σ_a(ε); and (v) for single‐bonded cyclic PFCs, substitution of CF₃ groups for F atoms increases (αw)_ther more than does an increase in molecular size; in double‐bonded cyclic compounds increase in ring size increases σ_a(ε) at thermal energies. The PFCs studied in this and the preceding paper have higher dielectric strengths than SF₆. This improvement in dielectric strength can be attributed to their large σ_a(ε) over a wider energy range (to ∼1.5 eV). Their use as unitary gases and/or as additives to multicomponent gas mixtures is discussed.