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

Abstract

Positronium collisions with rare-gas atoms are treated using the free-electron-gas approximation for exchange and correlation potential. The results confirm the absence of the Ramsauer-Townsend minimum in elastic scattering cross sections, but show lower cross sections in the lower-energy region when compared to previous pseudopotential calculations. This is explained by a more attractive ab initio correlation potential as compared to the previously used empirical potential. The results in the thermal energy region agree very well with most swarm measurements for all rare gas atoms. At higher energies the results are compared with beam experiments, and agreement for heavier rare gas atoms, Ar, Kr and Xe, is found to be very good. For He and Ne some discrepancies wth beam measurements are observed. This is explained by a poorer performance of the free electron gas potentials, based on the statistical Thomas-Fermi model, for systems with fewer electrons.

Resonance scattering of positronium atoms by nitrogen molecules

“…The calculations performed in the present paper can be improved by a more complete inclusion of the Pauli exclusion principle which can be done either by employing pseudopotentials with repulsive cores [36,37] or by using the orthogonalizing pseudopotential method [38,39] which has been successfully employed for treatment of Ps collisions with rare gas atoms [40]. Nevertheless we believe that our conclusions are quite general, and allow us to expect that generally vibrational dynamics in Ps-M collisions is not as pronounced as in corresponding e-M collisions for a general molecular target M. Indeed, no vibrational structure in Ps collisions with molecules has been observed so far, and no dissociative positronium attachment channels have been detected.…”

Confined variational calculation of o -Ps–He scattering properties

“…In addition, the energy dependence of σ m is found to be linear by Coleman et al [21] and quadratic by Engbrecht et al [24]. Calculations [25][26][27][28] support the ACAR results while raising doubts about the DBS results. Experimental and theoretical efforts are required to reconcile these findings for collision energies between 0.3 and 1.2 eV.…”

“…The main advantage of our method compared with the MBT, FTM, and FEG is that we treat the electrons of Ps and He equally. This equivalence can be illustrated by the probability [26], FTM [27], and FEG [28] for o-Ps-He scattering. k is given in units of a −1 0 and a b abbreviates a × 10 b .…”

“…Phase shifts obtained by the present advanced CVM with R 0 = 15a 0 (sufficient because the distortion of Ps is predominant), many-body theory (MBT) [26], frozen-target model (FTM) [27], and free-electron-gas (FEG) approximation [28] are compared in Table II. In the energy range considered, the D-wave phase shifts obtained are much smaller than the S-and P-wave phase shifts (contribute little to σ m ) and are not shown here.…”

Roadmap on photonic, electronic and atomic collision physics: II. Electron and antimatter interactions

“…As a consequence, despite the presence of extra channels (i.e. annihilation and Ps formation), the positron total cross-section is usually smaller than that for e − at intermediate energies, usually converging at high energies as illustrated in figure 16 for Ar and N 2 [116][117][118][119].…”