Comparative study of electron and positron scattering from benzene (C6H6) and hexafluorobenzene (C6F6) molecules

Total cross sections (TCSs) for electron and positron scattering from hexafluorobezene (C6F6) molecules have been measured by the linear transmission time-of-flight method and are presented. In addition, new systematic measurements have been also carried out for benzene (C6H6)-molecule targets. The impact energies are 0.4-1000 eV and 0.2-1000 eV for electron and positron scattering, respectively. For the case of C6F6, two resonance peaks have been observed in C6F6 electron TCSs: one at 0.8 eV attributed to the resonant capture of the incident electron into the π* orbital, with the formation of a transient C6F6- anion, and the broad one in the range above 7 eV showing weak spikes at 14 and 30 eV, of which the 14-eV one has been attributed to another negative-ion resonance formation with decomposition either through the reemission of the electron or through dissociative electron attachment leading to F-, C5F3-, and C6F5- fragmented ions. In contrast, the positron TCSs show no conspicuous strong structure but 2 to 3 weak shoulders overlaid on a broad (6-100)-eV peak arising from a series of electronic excitations, positronium formations, and ionizations. A close comparison with those for C6H6 sheds much light on better understanding of the underlying dynamics