Positron scattering by Ar, Kr and Xe was investigated considering two well-established semiempirical potentials with different descriptions of the asymptotic positron–atom scattering potential. Exploring the ultimate nature of semiempirical formulations, two independent semiempirical models were studied. In the first model, the potential parameters were fixed to reproduce the experimental values of the positron–atom scattering length, while, in the second, they were tuned to better fit experimental absolute folded differential cross sections through a χ2 approach. Results showed that the introduction of higher order polarisabilities and hyperpolarisabilities considerably improved the description of the forward scattering and the total and grand-total experimental low energy cross sections.

The aim of this work is to present and discuss the Ramsauer-Townsend effect in the context of low-energy positron scattering by rare gas atoms. Opposed to what happens in electron-atom scattering, the competition between the static repulsive and polarization attractive potentials makes the phenomenon improbable in positron case. Nonetheless, we show using a semiempirical potential formulation that, while the effect is explicitly observed in the total cross sections for He and Ne, for the heavier noble gases it becomes "hidden" or implicit. We show that as the atomic polarizability increases, the suppression of s-wave goes to higher energies due to the variation of the scattering length with the polarizability. No specific signature for the effect is found in the shape of the differential cross sections but curiously, while the effect is implicit in the total cross section for Ar, it generates a minimum structure in the momentum transfer cross section. The theme is presented for non-specialist audience with emphasis in basic atomic and scattering theories along with practical results, the main objective being to boost the traditional discussions with a new view on the subject.

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In this article we present the rotational excitation cross sections of N 2 by positron impact for energies between 1 and 10 eV. The cross sections were computed in the adiabatic rotational approximation within the many-body formalism of the Schwinger multichannel method. Our results show fortuitous agreement with previous rovibrational closed-coupling calculation and are higher in magnitude when compared to other similar calculation performed within the rigid rotor approximation. The convergence of static and static plus polarisation treatments suggests that dependence of polarisation for hexadecapole transitions may be neglected.