Electron attachment and detachment: C6F6

Abstract

Electron attachment to C6F6 is especially interesting because of the large change in symmetry between the neutral (D6h) and anion (C2v). We have made measurements of rate constants for electron attachment to C6F6 and thermal electron detachment from the parent anion, C6F6−, over the temperature range 297–400K, in 133Pa of He gas. A flowing-afterglow Langmuir probe (FALP) apparatus was used for this work. At 298K, the electron attachment rate constant is ka=8.6±3.0×10−8cm3s−1, and the detachment rate constant kd is approximately 35s−1. As the temperature increases kd increases rapidly, to about 3000s−1 at 400K. The attachment/detachment equilibrium implies that the electron affinity of C6F6 is 0.53±0.05eV. Density functional calculations were carried out in order to obtain thermal quantities needed to convert the equilibrium constant ka/kd into EA(C6F6). G3(MP2) calculations yielded an electron affinity of 0.454eV. The fluoride affinity of C6F6 was calculated to be 1.26eV at 298K using this same method. We expect the G3(MP2) results to be good within 0.1eV.