Total cross sections for positron and electron scattering from pyrimidine

Abstract

In this paper we report original measurements of total cross sections for positron scattering from the important biomolecule pyrimidine. The energy range of these measurements was 0.3–45 eV, while the energy resolution was ∼260 meV. In addition, we report theoretical results, calculated within the independent atom–screened additivity rule (IAM-SCAR) formalism, for the corresponding electron impact total cross sections. In that case the energy range is 1–10 000 eV. Total cross sections are very important input data for codes that seek to simulate charged-particle tracks in matter, as they define the mean-free path between collisions. As the present data and computations are to the best of our knowledge the first total cross sections to be reported for either positron or electron scattering from pyrimidine, they fill an important void in our available knowledge in the literature.

Total electron-scattering cross sections from pyrimidine as measured using a magnetically confined experimental system

“…For this estimation, our IAM-SCARD calculation, including rotational contributions treated as a dipole interaction, [10,11] is used as a reference. Figure 5 depicts the present experimental results together with our previously published IAM-SCAR(D) results [10,11], the recent scaled quasi-free-scattering model (SQFSM) total CS calculation of Ferraz et al [24], the low-energy Rmatrix calculations of Sanz et al [11], and experimental [24] and R-matrix [11] results in addition to the exact values.…”

“…Theoretical investigations on electron scattering from pyrimidine include our IAM-SCAR (independent atom model-screening-corrected additivity rule) calculations [10,11,13] and R-matrix calculations by Mašín and Gorfinkiel [22], Mašín et al [23], and Sanz et al [11]. In addition, we also note the Schwinger multichannel calculations from Palihawadana et al [14], and, most recently, scaled quasifree-scattering model calculations from Ferraz et al [24].…”

“…IV. An estimation of the systematic error can be derived from the results of our IAM-SCARD (IAM-SCAR including dipole interactions) calculations [10,14] (see Table I). …”

“…Pyrimidine belongs to the C 2v point group and exhibits a strong permanent dipole moment of between 2.28 and 2.39 D [7][8][9], which leads us to expecting a certain prominence of rotational excitations [10,11] in the scattering process at lower energies. We notice that in the last years, several electron-pyrimidine scattering studies have been published.…”

“…An extensive study on the VUV electronic state spectroscopy of pyrimidine has been reported by Ferreira da Silva et al [20] in the energy range 3.7-10.8 eV together with a comprehensive electron energy loss spectroscopy (EELS) of the singlet excitations in the range 2-15 eV. However, experimental total scattering CSs have, to the best of our knowledge, only been obtained for positrons as a projectile [10,21]. This is something of an oversight by the scattering community, because the total CS, being the sum of the integral cross sections for all possible scattering processes, represents a vital self-consistency check for those integral cross sections.…”