Elastic differential cross sections for C₄F₆ isomers in the 1.5–200 eV energy electron impact: Similarities with six fluorine containing molecules and evidence of F-atom like scattering

We report absolute elastic differential cross sections for electron interactions with the C₄F₆ isomers, hexafluoro-1,3-butadiene (1,3-C₄F₆), hexafluoro-2-butyne (2-C₄F₆), and hexafluorocyclobutene (c-C₄F₆). The incident electron energy range is 1.5–200 eV, and the scattered electron angular range for the differential measurements varies from 15° to 150°. In all cases the absolute scale of the differential cross section was set using the relative flow technique, with helium as the reference species. Atomic-like behaviour in these scattering systems is shown here for the first time, and is further investigated by comparing the elastic cross sections for the C₄F₆ isomers with other fluorinated molecules, such as SF₆ and C_nF₆ (n = 2, 3, and 6). We note that for all the six-F containing molecules, the scattering process for electron energies above 30 eV is indistinguishable. Finally, we report results for calculations of elastic differential cross sections for electron scattering from each of these isomers, within an optical potential method and assuming a screened corrected independent atom representation. The level of agreement between these calculations and our measurements is found to be quite remarkable in all cases.