R-matrix calculations for elastic electron and positron scattering from pyrazine: effect of the polarization description

Abstract

We present R-matrix calculations of electron and positron low energy scattering from the highly polarizable pyrazine molecule. We compare integral and differential elastic cross sections with experimental results and assess the quality of the models used for describing collisions of either projectile. Static-exchange-plus-polarization models give a good description of electron scattering (including that of shape resonances), whereas both the integral and small-angle differential cross sections are underestimated for positron collisions for the same models. We discuss whether the absence of a permanent dipole moment improves the comparison with experiment for this molecule, as well as future calculations that may improve the description of polarization effects and thus positron scattering. Graphical abstract

Improving polarization description in positron-molecule scattering: a model potential approach

“…In Figure (3) we present a comparison for the "folded" differential cross sections (FDCS) at some energies of interest, calculated in previous works with the SMC method (specially the one calculated with the best ab-initio polarization scheme, namely SP3) 25 , the R-Matrix method 26,27 the IAM-SCAR+I method 26 , with the differential cross sections calculated for the present article in the S+V cor approximation; plus the experimentally measured differential cross sections of Edwards et al 26 .…”

“…As of recent years, ab initio methods developed to describe positron scattering by molecules have struggled to describe existing experimental data (integral cross sections, differential cross sections and bound state energies when relevant), particularly for nonpolar molecules. The main problems in these results are in the low energy regime (below 20 eV), in which the calculated data significantly underestimates the experimental results even when the Ps formation channel is closed 19,27 . This can be also associated with a lower than expected intensity of the calculated differential cross sections in lower angles 25,27 .…”

“…The main problems in these results are in the low energy regime (below 20 eV), in which the calculated data significantly underestimates the experimental results even when the Ps formation channel is closed 19,27 . This can be also associated with a lower than expected intensity of the calculated differential cross sections in lower angles 25,27 . In the description of the calculated bound states, it is also possible to notice that the calculated energies are also lower than experimentally observed 24 .…”

Molecular collisions, photoionization and dynamics: honouring Professor Vincent McKoy

“…A high-resolution, variable-energy electron beam from a Penning-Malmberg (Surko) buffer-gas trap has been reported by Buckman and co-workers [25]. The investigation of the elastic scattering of low-energy electrons and positrons by pyrazine (isomer of C 4 H 4 N 2 ) was carried focusing on the description of polarisation effects [26]. Freitas and co-workers obtained elastic cross sections for the scattering of low-energy electrons by cubane (C 8 H 8 ) and discussed the shape resonance spectra and the presence of a Ramsauer-Townsend minimum and of a virtual state [27].…”

Low-Energy Positron Scattering by Pyridine and Aniline

“…They also reported elastic DCSs for energies from 1 up to 20 eV, which presented some (not expected) agreement with previous data for pyrimidine. Graves and Gorfinkiel discussed the description of polarization effects in R-matrix calculations for positron and electron scattering by pyrazine.…”