Ab initio electron-molecule scattering theory including polarisation: elastic scattering and rotational excitation of H₂

An ab initio L 2 basis-set theory for electron-molecule scattering is proposed. All terms of the potential (static, exchange and polarisation) are included. The T-matrix expansion technique of Rescigno et al. (1974) is extended to include polarisation via a one-electron optical potential, which is expanded in a diagrammatic perturbation series. Integral and differential cross sections for e-H 2 elastic scattering and rotational excitation at electron energy 0.6-10 eV are calculated with the lowest-order polarisation diagrams. Very good agreement with experiment is obtained for elastic scattering over the whole range and for rotational excitation above 4 eV.