Positronium Negative Ion Embedded in Non-ideal Classical Plasmas: Doubly Excited Singlet S States

The effects of the non-ideality (NI) of the classical plasmas on the doubly excited singlet S states in the positronium negative ion (Ps\(^-\)) are investigated. The organised effect of the plasma is taken care of by means of a pseudopotential which is characterised by the Debye length D and the non-ideality parameter \(\gamma \). Using an extensive wavefunction within the framework of the stabilization method, it has been possible to identify four doubly excited states (DES) in Ps\(^-\). The convergence of the energy and the width of those states are corroborated by increasing the number of terms in the wavefunction. Our present calculation for the plasma-free case reproduces the established results. An inclusive study is made to quantify and qualify the changes experienced by the energies and the widths of those states due to the influence of the NI over a wide range. It is observed that the energy of each DES increases and the width of each DES diminishes due to the effect of the increasing NI of the plasma.