Positron scattering from pyridine

Abstract

We present a range of cross section measurements for the low-energy scattering of positrons from pyridine, for incident positron energies of less than 20 eV, as well as the independent atom model with the screening corrected additivity rule including interference effects calculation, of positron scattering from pyridine, with dipole rotational excitations accounted for using the Born approximation. Comparisons are made between the experimental measurements and theoretical calculations. For the positronium formation cross section, we also compare with results from a recent empirical model. In general, quite good agreement is seen between the calculations and measurements although some discrepancies remain which may require further investigation. It is hoped that the present study will stimulate development of ab initio level theoretical methods to be applied to this important scattering system.

Theoretical study on positron scattering by benzene over a broad energy range

“…[21], by necessity coinciding with the well-known Ps formation threshold of p = I − 6.8 eV (where I = ionization threshold), for lower energies and the lowest optically allowed excitation transition for higher impact energies but applying the smooth tran-sition in threshold energy from low to high impact energy as proposed in Ref. [23]:…”

“…It has been successfully applied in preceding studies for several biologically relevant molecules (see Ref. [23] and references therein), typically in the range of 0.1-to 10 000-eV incident energy.…”

“…However, owing to the challenging nature of representing the Ps formation channel, the definition of the threshold energy for the absorption potential can be critical. Our recent improvements to the treatment of Ps formation were outlined in detail previously [22,23]. In brief we maintain the energy dependent threshold (E ) defined in Ref.…”

Positron interactions with nitrogen and oxygen molecules: elastic, inelastic and total cross sections

“…The IAM-SCAR+I method for the calculation of positron scattering cross sections has been improved in 2016, as outlined in our paper from Blanco et al [8]. This method builds on our previous work [4,11,12,14,15,[20][21][22][23][24] for both electrons and positrons, and has been used successfully in the past for biologically relevant molecules such as water [8,25], pyrimidine [26][27][28], pyridine [29], benzene [30], diatomic oxygen [24,31], tetrahydrofuran [32], macromolecules [21] and many more, typically in the range of 0.1 to 10000 eV incident energy.…”

“…For O and N the dipole plus quadrupole polarized orbital potentials of Ne (accurate against measurement [35]), are scaled so that they fit to the calculations of N and O presented in Reinsch and Meyer [36] and Werner and Meyer [37]. This method has been previously introduced and tested and was shown to produce good elastic scattering cross sections for positron impact [24,29], as well as reproducing the expectation value of the orbital radius for various oxygen orbitals [24].…”