Low-energy positron scattering from gas-phase benzene

Abstract

In this paper we are presenting calculations of the elastic cross section of positrons with gasphase 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.

Elastic Scattering of Slow Positrons by Pyrazine

“…In this panel we also compare the present cross sections with results for pyrimidine and benzene, both obtained with the SMC method. , The results obtained with the SP3 scheme agree well in shape and magnitude with benzene, and is lower than the cross section of pyrimidine as expected, because of the dipole moment of this molecule. It is worth mentioning that for benzene, the elastic results obtained with the independent atom model with screening-corrected additivity rule (IAM-SCAR) and with model potential calculations by Occhigrossi and Gianturco, agree well with the SMC results, while the “enhanced” R -matrix results obtained by Franz and Franz are bigger. In the lower panel of Figure we compare our SP3 result with the total cross section (TCS) measurement by Zecca et al and with the experimental quasi-elastic data of Palihawadana et al Additionally, we compare our pyrazine results with results for benzene, namely, the experimental TCS data of Zecca et al and Sueoka .…”

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

“…Whereas on the whole, this description no longer seems to pose serious limitations to the modelling of electron scattering, this is not the case for positrons, and this holds true for several of the methods mentioned above. Attempts have been made to improve and modify the approaches: for example, the use of atomic basis functions placed on additional 'dummy' centres in the SMC method [9] or use of a semi-empirical scaling factor to increase the electronpositron attraction integrals in R-matrix calculations [8] that improved their accuracy for a range of molecules [10,11]. Use of pseudostates has also been tried in Rmatrix calculations to improve polarization description.…”

Synthesis and Reactivity of Cationic Boron Complexes Distorted by Pyridine‐based Pincer Ligands: Isolation of a Photochemical Hofmann–Martius‐type Intermediate

“…[17] Cationic boron compounds have been compiled in a recent review. [22] As 2 a-c comprise the first family of cationic pincer-distorted boron compounds, the electronic structure of 2 a was investigated via density functional theory (DFT) calculations (see the Supporting Information (SI)). A natural population analysis calculation yielded a charge of 1.14 on the boron atom of 2 a.…”