The total cross-section of positronium scattering from molecular oxygen has been measured in the
velocity range 0.27 − 1.50 a.u. (energy range 2 − 61 eV) and found to be close to the corresponding
equivelocity electron cross-section above 0.87 a.u. (20 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 O−
2
formation and positronium
break-up 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
