Elastic scattering and rotational excitation of Li2 by positron impact

We report an ab initio and model potential investigation of elastic and rotational excitation cross sections for positron impact with Li2 molecule in the energy range from 0.1 to 10.0 eV. The ab initio cross sections were calculated with the Schwinger Multichannel Method, while the model potential calculations were performed with the Method of Continued Fractions, applying the correlation-polarization interaction known as PCOP. The converged elastic cross sections suggest a spherical polarizability for Li2 between 150 and 160 a03, a value considerably lower than the experimental one (≈216 a03). Rotational excitation cross sections obtained corroborate previous results available, with some discrepancy for the quadrupolar transition for energies below 3 eV. Our results indicate that such divergence comes from the consideration of a correlation-potential properly designed to treat positron-molecule scattering.