Jennifer E. Blackwood

Positronium scattering by Ne, Ar, Kr and Xe in the frozen target approximation

A full-electron coupled-state treatment of positronium (Ps)-inert gas scattering is developed within the context of the frozen target approximation. Calculations are performed for Ps(1s) scattering by Ne and Ar in the impact energy range 0-40 eV using coupled pseudostate expansions consisting of nine and 22 Ps states. The purpose of the pseudostates is primarily to represent ionization of the Ps which is found to be a major process at the higher energies. First Born estimates of target excitation are used to complement the frozen target results. The available experimental data are discussed in detail. It is pointed out that the very low energy measurements (≤2 eV) correspond to the momentum transfer cross section σmom and not to the elastic cross section σel. Calculation shows that σmom and σel diverge very rapidly with increasing energy and consequently comparisons of the low-energy data with σel can be very misleading. Agreement between the calculations and the low-energy measurements of σmom, as well as higher energy (≥15 eV) beam measurements of the total cross section, is less than satisfactory. Results for Ps(1s) scattering by Kr and Xe in the static-exchange approximation are also presented.

Reply to Comment on ‘Positronium scattering by Ne, Ar, Kr and Xe in the frozen target approximation’

A numerical inaccuracy in the static-exchange calculation of Blackwood et al (2002 J. Phys. B: At. Mol. Opt. Phys. 35 2661) for Ps(1s)–Xe scattering is corrected. The corrected result now conforms to the same pattern as He, Ne, Ar and Kr.

The estimation of potential energy curves for diatomic molecules

The Fourier grid method is used to deduce potential energy curves from spectroscopic data. The results are compared with those of ab initio calculations for H2 and with RKR method data for Na2 .

Positronium—atom scattering

Results of recent large coupled-pseudostate calculations of Ps scattering by H and He are presented. The parlous state of both theory and experiment for He is highlighted.