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Journal of Physics: Conference Series
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Electron impact ionization of pyrimidine: differential and total cross
sections
To cite this article: L Mouawad et al 2020 J. Phys.: Conf. Ser. 1412 152073
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ICPEAC2019
Journal of Physics: Conference Series 1412 (2020) 152073
IOP Publishing
doi:10.1088/1742-6596/1412/15/152073
1
Electron impact ionization of pyrimidine: differential and total cross
sections
L Mouawad1∗, P -A Hervieux1†, C Dal Cappello2, J Pansanel3, V Robert4and Z El
Bitar3
1Universit´e de Strasbourg, CNRS, IPCMS UMR 7504, F-67000 Strasbourg, France
2Universit´e de Lorraine, CNRS, LPCT UMR 7019 , F-57000 Metz, France
3Universit´e de Strasbourg, CNRS, IPHC UMR 7178, F-67000 Strasbourg, France
4Universit´e de Strasbourg, CNRS, Laboratoire de Chimie Quantique UMR 7177, F-67000 Strasbourg, France
Synopsis We provide theoretical cross sections for the ionization of pyrimidine by electron impact. The
theoretical framework is based on a quantum approach making use of particular tools to overcome the computing
challenges. The developed methodology allows to determine not only the total but also the triple, double and
simple differential cross sections. This approach was previously used to calculate the triple differential cross
sections of many molecules. Here, we demonstrate that it can be used to calculate more integrated cross sections
of a molecule of biological interest: pyrimidine.
Providing cross sections for the electron im-
pact ionization of biological molecules has be-
come an urgent requirement for valid investiga-
tions of particle interactions within the biolog-
ical medium. Due to the lack of cross section
data for complex biological molecules, interac-
tion cross sections with water are often used to
model interactions in living tissue. However, re-
cent studies show that using water to mimic bi-
ological systems is not quantitatively correct [1].
We propose a methodology to calculate differen-
tial and more integrated cross sections for the
ionization of biologically relevant molecules by
electron impact [2,3]. It is based on a distorted
wave model (DW) within the framework of the
First Born Approximation. We show here the re-
sultant cross sections for pyrimidine: a structural
unit of DNA and RNA bases thymine, cytosine
and uracil. In figure 1 we compare the triple
differential cross sections (TDCS) obtained with
the present model (solid line) to those computed
using the orientation averaged molecular orbital
(OAMO) approximation (dashed line) and the
experimental data from [4]. The OAMO approx-
imation was proposed as a solution to overcome
the difficulty of calculating cross sections for an
average molecular orientation by performing this
average on the level of the molecular wave func-
tions. It was used to determine the TDCSs for
many molecules but was found to deplete im-
portant information about the molecular orbital
structure. Figure 1 shows that the cross sec-
tions calculated with the DW model are in better
agreement with the experimental data.
Figure 1. Summed TDCSs for the electron ioniza-
tion of pyrimidine orbitals 10a1, 1b1and 6b2calcu-
lated with the DW (solid line) approach, compared
to OAMO TDCSs (dashed line) and experimental
data (solid circles) from [4].
References
[1] Fuss M C et al 2015 J. Appl. Phys. 117 214701
[2] Mouawad L et al 2017 J. Phys. B 50 215204
[3] Mouawad L et al 2018 J. Phys. B 51 175201
[4] Builth-Williams JD et al 2012 J. Chem. Phys.
136 024304
∗E-mail: lena.mouawad@hotmail.com
†E-mail: paul-antoine.hervieux@ipcms.unistra.fr
