Pseudostate effects on positron-helium excitation cross sections at intermediate energies

Abstract
Results of two five-state close-coupling (5CC) calculations of positron excitation of helium (11S to 21S,21P) at energies from 40 to 200 eV are presented and compared with an earlier 3CC calculation. In contrast to the e- case, inclusion of k1P and 41S pseudostates increases the cross sections (by 40% at 60 eV). For the 21P excitation the effect is almost entirely due to the k1P pseudostate. The e+ cross sections are substantially larger than those for e-. Total cross sections are given, but are poor below 100 eV due to neglect of positronium formation.

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