DIFFERENTIAL CROSS-SECTIONS FOR ELASTIC POSITRON-H-2 COLLISIONS USING THE R-MATRIX METHOD

Results are presented for positron-H 2 collision cross sections for energies below the positronium formation threshold. Calculations are performed with a variety of target representations, including full configuration interaction within a basis of Slater-type orbitals, and several models. The most sophisticated model includes the use of pseudo-excited electronic states of the target to account for intermediate-range polarisation effects. Short- and long-range polarisation effects are also considered. Calculations are performed for Σ g +, Σ u +, Π u, Π g, Δ g and Δ u symmetries which are combined to give differential cross sections as a function of energy. These calculations underestimate the Σ g + eigenphase sum but perform better for the higher symmetries. The differential cross sections show a minimum for angles about 45° which should be amenable to experiment. A computationally more efficient reformulation of the positron-molecule scattering problem is presented within the R-matrix method. Corrections are given for some previously published results. © 1990 IOP Publishing Ltd.