Positron-lithium scattering at low and intermediate energies

Positron-lithium scattering has been investigated using the three-state [Li(2s), Li(2p), and Ps(1s)] close-coupling approximation. Calculations have also been carried out by using the static, coupled static, and Born approximations. Elastic (2s-2s), excitation (2s-2p), and Ps-formation cross sections are reported up to an incident energy of 100 eV. The effect of the Ps-formation channel on elastic scattering is found to be pronounced at low incident energies, and this effect is not negligible even up to 50 eV. The positronium formation cross section is reduced appreciably in the energy region 1.0--20.0 eV when the 2p state is included in the expansion scheme.