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 (<10−3 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 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, 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 σa(ε) vary only slightly among these compounds, the magnitude of σa(ε) depends strongly on structure.

Elastic differential cross sections for C4F6 isomers in the 1.5–200 eV energy electron impact: Similarities with six fluorine containing molecules and evidence of F-atom like scattering

“…Such TNIs may decay in the elastic or inelastic channel but may also lead to a metastable anion or to dissociation of the molecule (dissociative electron attachment) producing neutral products and fragment anions. [19][20][21] At low electron impact energies, C 4 F 6 isomers exhibit resonance features in the TCSs between 1 and 15 eV, as most noticeable in Fig. 4 for 1,3-C 4 F 6 and 2-C 4 F 6 in the incident energy range between 2 and 10 eV.…”

Chapter 3: Trifluoromethyl Sulphur Pentafluoride, SF5CF3: Atmospheric Chemistry and Its Environmental Importance via the Greenhouse Effect

“…A small hole in the Faraday plate allows anions formed within the drift tube to enter a differentially-pumped region and a quadrupole mass spectrometer. The product anions formed from electron attachment can thus be determined, the major advantage of this instrument compared to more conventional electron swarm apparatus [61].…”

Electron collisions with octafluorocyclobutane, c-C4F8

“…5,8,9,[14][15][16][17][18][19][20][21][22][23][24] Many of these studies focused on the nondissociative attachment of electrons at very low energies, forming metastable C 4 F 8 Ϫ ions with a lifetime of 10 s or more; 14,17,21 the large cross section for this process accounts for the excellent dielectric properties of c-C 4 F 8 . At higher energies, several resonant peaks are observed in dissociative attachment, with F Ϫ being by far the principal ionic fragment produced, 5 although larger anions are also formed.…”