Near-threshold electron impact doubly differential cross sections for the ionization of neon and xenon

Abstract

Normalized doubly differential cross sections (DDCSs) for the electron impact single ionization of Ne and Xe are presented. The Ne measurements are taken at incident energies of 23.5 eV, 25 eV, 30 eV and 40 eV while the Xe measurements are taken at 14 eV, 15 eV and 20 eV. Scattering angles in the experiment range from 15° to 120°. The measurements use a moveable target method for an accurate determination of the experimental background. Normalization of the differential data is initially made to available experimental cross sections for excitation of the ground np6 to the np5 (n + 1)s excited states of the noble gas and then, if necessary after integration, to available experimental total ionization cross sections. We show that our single differential cross sections, derived from integrating the DDCSs, show a convex profile (frown) for Ne whereas they are concave (smile) for Xe similar to what is observed for He and we suggest a tentative mechanism for this effect.