Low-energy elastic electron scattering by tetrafluoromethane (CF4)

Abstract

We report cross sections for electronically elastic electron scattering by CF 4 from 1 to 40 eV, calculated within the static-exchange approximation using the Schwinger multichannel method. Although the static-exchange approximation does not give results that are accurate in detail below 20 eV, it is useful in understanding resonant features in the elastic and vibrationally inelastic cross sections. Above 20 eV, where the static-exchange approximation is more reliable, we derive a dissociation cross section in fair agreement with experiment by subtracting our result from the measured total cross section. We compare our integral and differential cross sections with the results of recent elastic and vibrationally inelastic scattering experiments.

Photoionization cross section and angular distribution calculations of carbon tetrafluoride

“…43 The use of the SAOP and LB94 xc potentials provides a partial screening of the hole formed during the photoionization process, while the screening is completely lacking in a frozen core formalism; this could partially explain energy shifts between KS and FCHF profiles. Moreover, the FCHF results fail to predict the correct symmetry of resonant states characterized in previous ab initio electronmolecule scattering calculations 65,66 and confirmed by our DFT calculations ͑vide infra͒. One could speculate that deficiencies in the FCHF potential prove unusually large for CF 4 , but also accurate experimental cross section measurements would be needed for a complete assessment of the performances of the KS and FCHF methods for this particular case.…”

Low-energy electron scattering by C2HF5

“…1 is artifactual. It is also important to note that, in the related fluorocarbon CF 4 , similar resonant peaks are seen in the fixed-nuclei elastic cross sections computed by various methods, [28][29][30][31] but not in the measured vibrationally elastic cross section; 32,33 rather, in CF 4 one finds strong resonant enhancement of the vibrationally inelastic cross sections 32,34 in the relevant energy range. We therefore speculate that much, if not most of the resonant enhancement of the C 2 HF 5 FN elastic cross section, may likewise contribute to vibrational excitation.…”

Low-energy electron collisions with sulfur hexafluoride, SF6

“…Because we neglect nuclear motion, the electronically elastic cross section we obtain does not distinguish between the vibrationally elastic and vibrationalexcitation cross sections. In CF 4 , for example, shape resonances in our computed elastic cross section 11 were not seen in the measured vibrationally elastic cross section 12,13 but were quite prominent in the vibrational-excitation 12,14 and total-scattering 15 cross sections. At very low impact energies, a fixed-nuclei description of SF 6 scattering is certain to be qualitatively incorrect, because the dominant process ͑forma-tion of metastable anions͒ involves nuclear motion.…”