Experimental and theoretical investigation of the triple differential cross section for electron impact ionization of pyrimidine molecules

Abstract

Cross-section data for electron impact induced ionization of bio-molecules are important for modelling the deposition of energy within a biological medium and for gaining knowledge of electron driven processes at the molecular level. Triply differential cross sections have been measured for the electron impact ionization of the outer valence 7b2 and 10a1 orbitals of pyrimidine, using the (e, 2e) technique. The measurements have been performed with coplanar asymmetric kinematics, at an incident electron energy of 250 eV and ejected electron energy of 20 eV, for scattered electron angles of −5°, −10°, and −15°. The ejected electron angular range encompasses both the binary and recoil peaks in the triple differential cross section. Corresponding theoretical calculations have been performed using the molecular 3-body distorted wave model and are in reasonably good agreement with the present experiment.

Dynamical (e,2e) studies of tetrahydrofurfuryl alcohol

“…Both are five membered heterocyclic ether compounds and in THFA a hydrogen atom on the alphacarbon is substituted by a CH 2 OH group. Interestingly, much narrower binary peaks have been observed both for ionization of the HOMO in pyrimidine 60 and for the inner valence orbitals in thymine, 61 again under similar kinematics. This observation is possibly related to the structure of the molecular rings in pyrimidine and thymine, which are both six membered ring type structures.…”

A dynamical (e,2e) investigation of the structurally related cyclic ethers tetrahydrofuran, tetrahydropyran, and 1,4-dioxane

“…The absence of any important theoretical recoil peak contribution has also been observed in our earlier studies on large biomolecules. 9,10,15 This is attributed to weak electron-nuclear scattering arising from the need to spread the nuclear charge in the calculation over large spherical shells, in order to perform the spherical averaging over the random orientation of the molecule. The key to unlocking this information may involve considering the localized ionization of the lone-electron pair on an oxygen atom, however, such calculations are limited by the complexity in performing scattering computations on open-shell targets.…”

“…Indeed, this kinematical condition has been most interesting in terms of our earlier dynamical (e,2e) studies on large biomolecules. [8][9][10][11][12][13][14] …”

“…Such studies represent an important step in understanding how the structure of a species can influence the electron scattering phenomena. In this vein, we have recently extended some of our earlier studies on individual biomolecules [8][9][10][11][12][13][14] to chemically similar compounds in an attempt to further understand the role of structure and kinematics on the dynamics of electron-impact ionization. 15 Building on that work, we present a dynamical (e,2e) investigation to compare the electron-impact ionization process across a series of cyclic ethers: tetrahydrofuran (THF, C 4 H 8 O), tetrahydropyran (THP, C 5 H 10 O), and 1,4-dioxane (C 4 H 8 O 2 ).…”

Differential cross sections for the electron impact excitation of pyrimidine

“…This has led to a number of recent electron scattering experiments from pyrimidine. These have included low-and intermediate-energy elastic electron scattering experiments, 10, 11 measurements of the threshold-electron excitation spectra, intermediate-energy electron energy loss spectra, 3 total cross sections, 12 dynamical and binary tripledifferential cross sections, 13,14 and electron energy loss spectra of pyrimidine condensed on thin argon films. 15 Recently, we have published 16 data for electron-impact excitation of two excitation features of pyrimidine at 15 and 30 eV, in a comparative study with benzene relating to the nature of electron induced π -π * transitions in aromatic compounds.…”