Positron collisions with alkali atoms at low and intermediate energies

The close-coupling approximation has been used to investigate positronium formation into the n = 1 and n = 2 levels and the excitation of the target in positron-sodium and positron-potassium collisions at impact energies up to 60 eV. The interaction between the positron and the alkali target atom is represented by a model potential obtained using a single-electron approximation. The 3s, 3p, 4s and 4p states of sodium and the 4s, 4p, 5s and 5p states of potassium have been included. The effect on elastic scattering and excitation due to the coupling to positronium formation channels has been studied by adding the positronium 1s, 2s and 2p eigenstates to the expansion. (author)