ELECTRON-ATTACHMENT TO PERFLUOROCARBON COMPOUNDS .1. C4F6,2-C4F6,1,3-C4F6,C-C4F8 AND 2-C4F8

Electron attachment rates αw, as a function of the pressure-reduced electric field E/P298 and mean electron energy 〈ε〉 have been measured for trace amounts (<10-3 Torr) each of c-C 4F6 (perfluorocyclobutene), 2-C4F6 (perfluoro-2-butyne), 1,3-C4F6 (perfluoro-1,3-butadiene), c-C4F8 (perfluorocyclobutane), and 2-C4F 8 (perfluoro-2-butene) in mixtures with N2 (pressures 500-2000 Torr) and Ar (pressures 500-1500 Torr) at T = 298°K. The thermal attachment rates for these molecules were found to be 4.89 × 10 9, 1.77 × 109, 4.26 × 109, 4.05 × 108, and 1.56 × 109 sec-1 Torr-1, respectively. From the αw(〈ε〉) data, the attachment cross sections σa(ε) as a function of electron energy ε have been determined using the swarm-unfolding technique and are reported. For all five perfluorocarbon molecules, σa(ε) are very large. They exhibit three distinct negative ion resonances with maxima at: ∼0.0, 0.19, and 0.80 eV for 2-C4F6; ∼0.0, 0.17, and 1.04 eV for 1,3-C4F6; ∼0.0, 0.22, and 0.48 eV for c-C4F8; and -∼.0, 0.18, and 0.59 for 2-C 4F8. For c-C4F6, only a shoulder with a possible maximum at ∼0.14 eV was observed, in addition to the maxima at ∼0.0 and 0.71 eV. Although the positions of the maxima in σa(ε) vary only slightly among these compounds, the magnitude of σa(ε) depends strongly on structure. © American Institute of Physics.