Contrasting low-energy behaviour in total cross sections for electron and positron scattering from benzene molecules

Abstract

Marked differences of a rise and a drop in total cross sections below 1 eV between electron and positron impacts, respectively, are experimentally observed for benzene. The present result for electron scattering becomes flat below 1 eV, and smoothly connects with that of Gulley et al (1998 J. Phys. B 31 2735), which shows a sharp rise below 500 meV. The present result for positron reaches a peak at around 1.5 eV and drops relatively sharply below this energy. These remarkably opposite characteristics, i.e., a sharp rise or drop with respect to decreasing incident energy, are attributable to the delicate balance between the attractive and repulsive interactions which results in a virtual state for electron impact, hence causing the sharp increase while the near-zero scattering for positron impact causes the sharp drop.