Abstract
In this paper we are presenting calculations of the elastic cross section of positrons with gas-phase benzene for the energy range from 0.25 eV to 9.0 eV. The calculations are done with the molecular R-matrix method for positron-scattering from poly-atomic molecules using a scaling factor to scale the electron-positron interaction. The scaling factor influences the position of the poles of the R-matrix. We adjust the scaling factor is such a way, that the position of the lowest pole is similar to the proposed binding energy of around 150 meV, given by [J.A. Young, C.M. Surko, Phys. Rev. Lett 99, 133201 (2007)]. Below the threshold for positronium formation, we calculate elastic cross section in good agreement with experimental cross sections. Above the threshold for positronium formation we use the difference between the experimental total cross section data and our computed elastic cross section to provide a first estimation of the cross section for positronium formation.Graphical abstract
Highlights
Benzene is one of the simplest organic molecules
The target states are constructed from a complete active space configuration interaction (CAS-CI) wavefunction, where the complete active space is generated by distributing 4 electrons in 7 orbitals
The continuum basis set is contructed for 8s, 7p, 7d, 6f and 6g functions In Figure 1 the total elastic cross sections are shown for different values of the scaling factor f using the CAS-CI model
Summary
Benzene is one of the simplest organic molecules. It is an ideal model compound to study interactions of positrons with biological matter. Fedus [11] has analysed low-energy cross section data extract the scattering length with the modified effective range theory (MERT) [12]. As input for his MERT model he uses the scattering length obtained from the experimental binding energy of Young et al [6]. In this paper we present calculations of the elastic cross section of positrons with benzene molecules in the gasphase over the energy range from 0.25 eV to 9.0 eV. By using the scaling factor to move the lowest pole of the R-matrix to the value of the positron binding energy, we obtain an elastic cross section in good agreement with experimental data sets.
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