Positron?Lithium Inelastic Scattering with Polarisation Potentials

Abstract

Positron-lithium inelastic scattering is studied at positron energies ranging from 0·005 to 20 eV using the coupled static model. Two channels are open namely the elastic and positronium formation. The polarisation potentials of the Li atom in the first channel and that of the positronium atom in the second channel are taken into consideration in calculating the corresponding cross sections. The partial cross sections in each channel are calculated for eight values of the total angular momentum (0 ~.e ~ 7). In the elastic channel the total cross section Ull has its maximum value at the lowest energy, and decreases with an increase in positron energy Ki. The total positronium formation cross section has a small dip at 0·1 eV, and maximum value at Ki = 1 ·4 eV, and then decreases smoothly with e+ energy. We compare our results with those of Ward et al. (1989) where positronium formation is ignored. The agreement in elastic cross sections improves with e+ energy, while the total collisional cross sections have the closest agreement at 1·0 eV. From this comparison, we find that positronium formation is important in the very low energy region, and the role of the excitation cross section increases steadily with e+ energy.