Rotational excitation of tetrahedral molecules by positron impact in the Born approximation

Rotational cross sections of tetrahedral molecules for low energy positron impact is the theme of this work. The scattering model is based in the Born approximation combined to multipole formulation for the scattering potential. We choose the CH4 and CF4 molecules as model systems to illustrate the theory. We obtain analytical expressions for octupole and hexadecapole transitions in relative momentum and partial waves formulations. The dependence of the cross sections on the molecular multipole moments, as well as the incident particle energy is directly identified. Comparison to the ab initio results found in literature exhibit good agreement for positron-CH4 rotational cross sections.