Highly resolved absolute cross-sections for dissociative electron attachment to SF5CF3

Abstract

Using two complementary experimental methods, we have measured partial (mass-resolved) cross-sections for dissociative electron attachment to the molecule trifluoromethyl sulfurpentafluoride (SF5CF3) at the gas temperature TG=300K over a broad range of electron energies (E=0.001–12eV). The absolute scale for these cross-sections was obtained with reference to the thermal (T=300K) rate coefficient for anion formation (8.0(3)×10−8cm3s−1). Below 1eV, SF5− is the dominant product anion and formed through the lowest anion state which cuts the neutral SF5CF3 potential close to the S–C equilibrium distance. The highly resolved laser photoelectron attachment data exhibit a downward Wigner cusp at 86meV, indicating that the ν4(a1) vibrational mode is important for the primary attachment dynamics. Both SF5− and F− anions are formed with similar yields through the first excited resonance located near 3.6eV. Towards higher energies, the anions CF3−, SF4−, and SF3− are also produced. Summation of the partial cross-sections yields a total absolute cross-section for anion formation over the energy range 0.001–12eV. This is used to calculate the dependence of the rate coefficient for dissociative electron attachment over a broad range of electron temperatures for the fixed gas temperature TG=300K; good agreement is found between the calculated values and those obtained in a drift tube experiment. In addition to the experimental work, semiempirical R-matrix calculations have been carried out for the energy dependence of the cross-section for SF5− formation. The experimental findings are semi-quantitatively recovered.