Positronium scattering by polar molecules

Experimental measurements of the total cross section for scattering of Positronium (Ps) by various atomic and molecular targets are very similar to electron scattering cross sections above the Ps ionization threshold [1]. Using a Free Electron Gas model [2] we have previously calculated elastic scattering cross sections for Ps scattering by the homonuclear diatomic molecules N₂ and O₂ as well as CO₂ [3]. To obtain the total scattering cross section we added the Ps ionization cross section which was computed using the binary encounter method. Our calculations confirmed that the total cross section for electron and Ps scattering is similar above the Ps ionization threshold. The present target molecules provide a range of dipole moments from the weakly polar CO to the strongly polar LiF. We find that Ps scattering is similar to electron scattering when the cross sections areplotted as a function of projectile velocity for the targets with smaller dipole moments (CO, HCl). However, we do not see such a similarity for LiF which suggests that the similarity between electron and Ps scattering does not extend to highly polar targets. Below the Ps break-up threshold we observe resonance structures similar to those obtained earlier for the other molecular targets that we have studied.

¹S. J. Brawley et al., Science 330, 789 (2010). ²R. S. Wilde and I. I. Fabrikant, Phys. Rev. A 98, 042703 (2018). ³R. S. Wilde, H. B. Ambalapitiya and I. I. Fabrikant, Phys. Rev. A 104, 012810 (2021).