Positronium collisions with molecular nitrogen

Abstract

For many atomic and molecular targets positronium (Ps) scattering looks very similar to electron scattering if total scattering cross sections are plotted as functions of the projectile velocity. Recently this similarity was observed for the resonant scattering by the N 2 molecule. For correct treatment of Ps-molecule scattering incorporation of the exchange interaction and short-range correlations is of paramount importance. In the present work we have used a free-electron-gas model to describe these interactions in collisions of Ps with the N 2 molecule. The results agree reasonably well with the experiment, but the position of the resonance is somewhat shifted towards lower energies, probably due to the fixed-nuclei approximation employed in the calculations. The partial-wave analysis of the resonant peak shows that its composition is more complex than in the case of e−N 2 scattering.

Positronium collisions with rare-gas atoms: Free-electron gas plus orthogonalizing pseudopotential model

“…The correlation potential of refs. [17,18] is similar to the correlation potential for electron scattering derived by O'Connell and Lane [20].…”

“…The FEG correlation potential is free of adjustable parameters and exhibits a strong attraction at short distances. We have previously used this model to investigate Ps-N 2 scattering [18] and were able to reproduce the resonance structure seen experimentally there and obtained good agreement with experiment above the ionization threshold, although again, at lower velocities the calculated cross sections seem to be substantially larger than the experimental.…”

“…where V XC is the local exchange plus correlation potential derived in [18], and γP is an orthogonalizing pseudopotential as defined in [14,15,26]. In the remainder of this section we describe the FEG local exchange and correlation potentials and derive the expression for the OPP kernel.…”

“…The FEG model for the Ps-molecule scattering potential in refs. [17,18] is similar to the HFEGE model except that there is an additional contribution to the exchange potential due to the positron interaction with the target electrons. The correlation potential of refs.…”

The Hidden Ramsauer-Townsend Effect in Positron Scattering by Rare Gas Atoms

“…In a recent article, Wilde and Fabrikant [4] performed model calculations for positronium scattering by rare gas (Rg) atoms. In particular, attention was devoted to the problem of identification of RT minima in positroniumatom scattering.…”