Electron Attachment to C7F14, Thermal Detachment from C7F14–, the Electron Affinity of C7F14, and Neutralization of C7F14– by Ar+

Abstract

Rate coefficients and branching fractions have been measured for electron attachment to perfluoromethylcyclohexane, C(7)F(14), along with thermal detachment rate coefficients for C(7)F(14)(-), from 300 to 630 K, using a flowing-afterglow Langmuir-probe apparatus. The attachment rate coefficient at room temperature is 4.5 ± 1.2 × 10(-8) cm(3) s(-1) and increases with temperature at a rate described by an activation energy of 50 ± 25 meV. Thermal electron detachment is negligible at room temperature, but measurable at 600 K and above, reaching 2300 ± 1300 s(-1) at 630 K. Analysis of the attachment-detachment equilibrium yields EA(C(7)F(14)) = 1.02 ± 0.06 eV, in agreement with the literature value while more than halving the uncertainty. Implications of the measurement for the electron affinity of SF(6) are discussed. The dominant product of electron attachment is the parent anion, but C(6)F(11)(-) and C(7)F(13)(-) are also observed at very low levels (<0.1%) at room temperature and increase in importance as the temperature is increased, reaching ~10% each at 630 K. In the course of this work we have also measured rate coefficients for the neutralization of C(7)F(14)(-) by Ar(+) at 300, 400, and 500 K: 4.8, 3.5, and 3.1 × 10(-8) cm(3) s(-1), respectively, with uncertainties of ±5 × 10(-9) cm(3) s(-1).