LARGE BASIS CALCULATION OF POSITRON-HYDROGEN SCATTERING AT LOW ENERGIES

Calculations of low energy positron-hydrogen scattering using the clos e coupling approach are reported at low energies. The channel space in cludes nine physical hydrogen and positronium states and in addition t welve hydrogen and positronium pseudo-states. For energies below the p ositronium formation threshold, phase shifts are reported for J=0 to 6 and are believed to have an absolute accuracy of 0.0015 radian or bet ter. Elastic scattering and positronium formation cross sections in th e Ore gap for the J = 0 and J = 1 partial waves are essentially identi cal with previous Variational calculations. Total elastic and positron ium formation cross sections are reported at incident energies below t he ionisation threshold. Cross sections for the excitation of the H(n= 2), H(n=3) and Ps(n=2) levels are also reported over a restricted ener gy range, and the total reaction cross section has been computed and c ompared with experiment.