Elastic scattering of electrons (or positrons) from positronium and the photodetachment of the positronium negative ion

The authors report accurate variational calculations of the 1,3 S and 1,3 P phaseshifts for the elastic scattering of electrons (or positrons) by positronium up to the n=2 threshold. Higher-order phaseshifts are evaluated both in a static-exchange model and in an adiabatic-exchange model to give the total elastic, momentum transfer, ortho-para conversion and elastic differential cross sections. The positions of the minima in the elastic differential cross section are given for several values of k 2 . New 3 P resonances are reported. The 1 P continuum wavefunction is used together with an accurate variational wavefunction for the ground state of Ps - to obtain the photodetachment cross section of Ps - , and both length and velocity results are checked by evaluating the sum rule S -1 .