Electron attachment to perfluorocarbon compounds. I. c-C4F6, 2-C4F6, 1,3-C4F6, c-C4F8 and 2-C4F8

Abstract

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 (−3 Torr) each of c‐C₄F₆ (perfluorocyclobutene), 2‐C₄F₆ (perfluoro‐2‐butyne), 1,3‐C₄F₆ (perfluoro‐1,3‐butadiene), c‐C₄F₈ (perfluorocyclobutane), and 2‐C₄F₈ (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 4.89×10⁹, 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 σ_a(ε) as a function of electron energy ε have been determined using the swarm‐unfolding technique and are reported. For all five perfluorocarbon molecules, σ_a(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, 0.18, and 0.59 for 2‐C₄F₈. 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 σ_a(ε) vary only slightly among these compounds, the magnitude of σ_a(ε) depends strongly on structure.