Electron impact ionization and dissociation of molecules relevant to gaseous dielectrics

摘要

Molecules such as methane (CH_4),carbon-tetrafluoride (CF_4), the perfluoroalkanes (C_nF_2n+2, n=2,3,4), and sulfur-hexafluoride (SF_6) have received much attention because of their favorable electron transport properties in various applications such as gaseous dielectrics, plasma processing, and diffuse discharge switches. Ion formation processes involving SF_6 have been studied extensively in the past. A summary of available partial and total cross sections for the formation of positive ions from SF_6 can be found e.g. in the recent paper of Deutsh et al.~2. Negative ion formation processes have bene reviewed by Chriistophorou and co-workers~3. Negative ion formation processes have bene reviewed by processes involving the SF_x (x=1-5) free radicals or about the electron-impact dissociation of SF_6 into neutral ground-state fragments even though these are processes of great relevance for the understanding of the properties of gas mixtures containing SF_6. Sugai and co-workers~4 measured the relative cross sections for the formation of SF_x (x= 1-3) radicals following electron impact on SF_6. Recently, the fullerences C_60 and C_70 have been proposed as potential electron scavangers because of their large attachment cross sections at very low electron energies~5-7.