Third-order optical model analysis of e+or-H(2s), e+or-He(21S) and e+or-He(23S) elastic scattering at intermediate energies

Abstract
The authors study the elastic scattering of electrons by the metastable states H(2s), He(21S) and He(23S) at intermediate energies within the framework of the third-order optical potential theory. The first-, second- and third-order contributions to the optical potential are analysed separately, and are compared with the corresponding quantities for e-H(1s) and e-He(11S) elastic scattering. Results for positron impact scattering are also presented.