Positronium formation cross section for positron-lithium collisions

The hyperspherical hidden crossing method (HHCM) has been used to calculate the positronium formation cross section for positron-lithium collisions in the energy range 0-1.8 eV. Results for the s-, p- and d-wave positronium formation cross sections were previously reported; here we present new results for the f-wave. In energy range studied, we found that the Stückelberg phase ΔL varied only slightly with incident positron momentum ki and decreased in a systematic way with increasing partial wave L. The HHCM cross section for positronium formation (summed over the four partial waves) lies between experimental measurements of the lower and upper limits of this cross section; the f-wave contribution to the cross section dominates near the lithium excitation threshold.