R-matrix calculations of vibrationally resolved positron-N2scattering cross sections

The molecular R-matrix method has been used to perform ab initio positron-N 2 scattering calculations in the fixed-nuclei approximation. Various treatments of polarization and correlation effects have been studied, including the introduction of up to 22 polarized pseudostates. A model in which the N 2 comprised an SCF ground state and 10 excited pseudostates was adopted for 12 internuclear geometries ranging from 1.6 to 2.9 a 0 . Vibrationally elastic and inelastic cross sections are obtained using the adiabatic nuclei approximation and a non-adiabatic model. Non-adiabatic effects are significant for the v=0 to 1 cross section (and dominate the small v=0 to 2 result). Some early calculations at the equilibrium geometry (R=2.068 a 0 ) have been corrected.