Kinetic Energies of Ionization Products from Collisions of Ar–Ar, He–He below 150 eV c.m. Energy

Abstract

Measurements have been made of the energy spectra of ions and electrons produced in the collision of beams of neutral Ar of given energy (laboratory energy range 57–240 eV) with a gas of Ar and of neutral He (145–300 eV) with a gas of He. The energy dependence of the total cross section for ionization is consistent with previous results. The electron spectra from collisions of $\mathrm{Ar}+\mathrm{Ar}$ show peaks at 0, 6, and $\text{∼9\hspace{0.17em}}\mathrm{eV}$ . From this we estimate that about 15% of the Ar⁺ ions produced come from autoionizing states of Ar. For certain ranges of initial relative energy $\mathrm{Ar}–\mathrm{Ar}$ ionization occurs mostly in backscattering collisions. An analysis of the ion spectra of experiments at these initial relative energies (greater than 33 eV), made with a simple model, shows that most ions are produced by two curve crossings $\text{12±2}\mathrm{eV}$ and $\text{22±1}\mathrm{eV}$ above the ionization potential (15.8 eV).