Scattering of positronium atoms

Ortho-positronium-ortho-positronium (o-Ps-o-Ps) scattering is investigated using close coupling model. The following four basis sets have been employed: (1) Ps(Is)+Ps(Is) (2) Ps(Is,2s,2p)+Ps(Is,2s,2p) (3) Ps(Is,2s,2p)+ Ps(Is,2s,2p) and (4) Ps(Is,2s,2p, 3d) + Ps(Is,2s,2p, 3d) and convergent s-wave elastic scattering parameters for the spin alignment S = 0 and S = 2 have been reported up to the incident energy 3.4 eV. The present s-wave phase shifts for both the spin alignments are found to be in fare agreement with the existing elaborate theoretical predictions. In particular our S = 2 s-wave scattering length lies in the vicinity of the exact results. (C) 2004 Elsevier B.V. All rights reserved.