Binary-Encounter Model for Direct Ionization of Molecules by Positron-Impact

Małgorzata Franz,Jan Franz,Katarzyna Wiciak-Pawłowska

doi:10.3390/atoms9040099

Abstract

We introduce two models for the computation of direct ionization cross sections by positron impact over a wide range of collision energies. The models are based on the binary-encounter-Bethe model and take into account an extension of the Wannier theory. The cross sections computed with these models show good agreement with experimental data. The extensions improve the agreement between theory and experiment for collision energies between the first ionization threshold and the peak of the cross section. The models are based on a small set of parameters, which can be computed with standard quantum chemistry program packages.

Highlights

We present two new models for the computation of cross sections for direct ionization of atoms and molecules by positron-impact
The review by Brunger et al [1] recommends for the direct ionization of molecular hydrogen by positron impact the experimental cross section data from Fromme et al [13]
Recent calculations by Utamuratov et al [15] with the convergent close-coupling (CCC) method are closer to the data from Jacobsen et al [14] than to the data from Fromme et al [13]

Summary

Introduction

We present two new models for the computation of cross sections for direct ionization of atoms and molecules by positron-impact. The recent review articles by Brunger et al [1] and Ratnavelu et al [2] show only the sum of the cross sections for Ps-formation and direct ionization for the majority of targets. This shows the need for the development of an accurate theoretical model for the computation of the cross sections for direct ionization. Such a model can be used to deduct the cross section for Ps-formation from cross sections that cannot distinguish between different ionization channels

Objectives

Results

Conclusion