Electron attachment and detachment: cyclo-C 4F 4Cl 2

Abstract

Electron attachment to 1,2-dichlorotetrafluorocyclobutene (c-C 4F 4Cl 2) and electron detachment from the parent anion (c-C 4F 4Cl 2 −) have been studied over a temperature range from 295 to 556 K in a flowing-afterglow Langmuir-probe (FALP) apparatus. Electron attachment to c-C 4F 4Cl 2 over this temperature range yields only the parent anion in a helium buffer gas at 80–160 Pa pressure. The electron attachment rate constant was found to be independent of temperature over the range studied, at a value of (2.4±0.8)×10 −7 cm 3 s −1, that is, essentially upon every collision. The rate constant for electron detachment from c-C 4F 4Cl 2 − is strongly temperature dependent, being imperceptible at room temperature and climbing to a value of 3100±1200 s −1 at 511 K. The equilibrium constant obtained from these data yields the electron affinity (EA) of c-C 4F 4Cl 2 of 0.87±0.08 eV. G3(MP2) and density functional theory (DFT) calculations were carried out for the C 4F 4Cl 2 neutral, anion, and fragments in order to aid in interpreting the experiments. Both the G3(MP2) and DFT calculations yield values for EA(c-C 4F 4Cl 2), 0.79 and 0.93 eV, respectively, that are in good agreement with the experimental value. The calculations also show that there are no open exothermic dissociative electron attachment channels for c-C 4F 4Cl 2. Further, we present structures, atomic charges, dipole moments, heat capacities, and polarizabilities for these molecules. The results are contrasted with previous results on 1,2-dichlorooctafluorocyclohexene (c-C 6F 8Cl 2) and 1,2-dichlorohexafluorocyclopentene (c-C 5F 6Cl 2), both of which possess larger EAs.