Lowest lying doubly-excited P- and D-state resonances of Ps- in weakly coupled plasmas

The lowest-lying 1,3Po and 1De resonances of positronium negative ion, Ps-, in weakly coupled plasmas have been investigated employing the close-coupling approximation. Three different basis sets have been employed in the present study. The plasma screening condition obtained from the Debye-Huckel type potential is used to represent the interaction between the charged particles. The resonance energies and the corresponding widths of one 1Po, two 3Po, and one 1De resonant states associated with the n = 2 threshold of the positronium atom for various Debye lengths ranging from infinity to small values are reported. The 1Po resonance as well as the higher lying 3Po resonant state transforms to a shape resonance for denser plasma conditions. The 1De resonant state also changes to a shape-type resonance for very dense plasmas. (author)