Low-energy positronium scattering from O2

Abstract

The total cross section of positronium (Ps) scattering from molecular oxygen has been measured in the velocity range 0.27--1.50 a.u. (energy range 2--61 eV) and has been found to be close to the corresponding equivelocity electron cross section above 0.87 a.u. $(20\phantom{\rule{0.16em}{0ex}}\mathrm{eV})$, as previously found by Brawley et al., [Science 330, 789 (2010)]. However, below this value the cross section for positronium is observed to exceed that for electrons by up to a factor of 4 at the lowest energy. Measurements are compared to the predictions of low-energy resonant peaks in the elastic-scattering cross section calculated within a free-electron-gas model refined by applying corrections to the correlation energy for the interaction between Ps and the electron gas. Additionally, cross sections for ${\mathrm{O}}_{2}^{\ensuremath{-}}$ formation and positronium breakup have been calculated using a classical-trajectory Monte Carlo approach. Comparisons are made with earlier calculations and discussed in terms of both experimental and theoretical uncertainties.