Independent Atom Method Research Articles

Absolute differential cross sections for elastic scattering of electrons from pyrimidine

Differential cross sections (DCSs) for elastic scattering of electrons from pyrimidine $({\text{C}}_{4}{\text{H}}_{4}{\text{N}}_{2})$ are presented for incident energies from 50 to 300 eV. The measurements were performed using a cross beam technique, for scattering angles from $20\ifmmode^\circ\else\textdegree\fi{}$ to $110\ifmmode^\circ\else\textdegree\fi{}$. The relative DCSs were measured as a function of both the angle and incident energy and the absolute DCSs were determined using the relative flow method. The calculations of electron interaction cross sections are based on a corrected form of the independent-atom method, known as the screen corrected additivity rule procedure and using an improved quasifree absorption model. Calculated results agree very well with the experiment.

Absolute cross sections for elastic electron scattering from 3-hydroxytetrahydrofuran

The results of measurements and calculations of absolute cross sections for elastic electron scattering from the 3-hydroxytetrahydrofuran (3hTHF) (C4H8O2) molecule are reported. The measurements were performed using a crossed beam experimental setup, for an incident electron energy range of 40–300 eV and an overall scattering angle range of 10°–110°. Relative differential cross sections (DCSs) were measured both as a function of the angle and the incident energy and the absolute DCSs were determined using the relative flow technique. The calculations of molecular cross sections are based on a corrected form of the independent-atom method, known as the screen corrected additivity rule (SCAR) procedure and using an improved quasifree absorption model. Additional calculations are also done to investigate the influence of rotational excitations and low-angular behavior of SCAR DCSs. The calculated dataset includes differential, integral and total cross sections in the energy range from 5 eV to 10 000 eV. The present results are discussed regarding the most recent low-energy elastic DCSs for 3hTHF (Vizcaino et al 2008 New J. Phys. 10 053002), as well as the recent DCSs for molecules of similar structure (tetrahydrofuran and tetrahydrofurfuryl alcohol).

Elastic scattering of electrons from alanine

Differential cross sections (DCSs) for elastic scattering of electrons from alanine, have been measured using a crossed beam system for incident energies between 20 and 80eV and scattering angles from 10° to 150°. The experimental data were placed upon an absolute scale by normalisation to calculated absolute integral cross sections obtained using the corrected independent-atom method incorporating an improved quasifree absorption model. The calculated data-set includes DCSs and integral elastic and inelastic cross sections in the incident energy range between 1 and 10,000eV. These theoretical results are found to agree very well with the experimental data both in the shape and magnitude of DCSs except at the smallest scattering angles.

Elastic scattering of electrons from tetrahydrofurfuryl alcohol

Differential cross-sections (DCSs) for elastic scattering of electrons from tetrahydrofurfuryl alcohol (THFA), which can be considered as an analogue molecule to DNA sugar deoxyribose, were determined using crossed beam measurements for incident energies from 40 eV to 300 eV and scattering angles from 30° to 110°. The relative DCSs were measured both as a function of incident electron energy and scattering angle, allowing absolute calibration of the whole data set via normalization to a single point. The absolute calibration has been performed according to calculated absolute DCSs obtained by the corrected independent atom method using an improved quasifree absorption model. The calculated data-set includes DCSs and integral elastic and inelastic cross-sections in the incident energy range from 5 eV to 5000 eV. The theoretical results agree very well with the experimental ones, regarding the shape of DCSs. Moreover, the same theoretical procedure has been used to obtain DCSs for elastic electron scattering from a simpler deoxyribose analogue tetrahydrofuran (THF), which agree very well, both in shape and on the absolute scale, with the recent experimentally obtained absolute DCSs [A.R. Milosavljevic et al., Eur. Phys. J. D 35, 411 (2005)]. The present results are also compared with the recent theoretical data for THF and THFA. Finally, according to both experimental and theoretical data, the DCSs for elastic electron scattering from THFA and THF molecules appear to be very similar both in shape and absolute scale.

Cross sections for electron scattering from selected components of DNA and RNA

Differential and integral cross sections for elastic collisions between electrons and selected analogues of components of the backbone of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are calculated using the independent atom method with a static-polarization model potential. They are presented for tetrahydrofuran, 3-hydroxytetrahydrofuran, α-tetrahydrofurfuryl alcohol, and phosphoric acid within 50–2000eV electron energy range. Cross sections for electron-impact ionization of these molecular targets are also derived using the binary-encounter-Bethe model in the energy range from the ionization threshold to 4000eV. Single electron-impact ionization cross sections for the sugar-phosphate unit are also approximately derived. The results are compared with available data.

Electron collisions with nitrogen trifluoride(NF3)molecules

Absolute total cross sections (TCS's) for $0.5--370\text{\ensuremath{-}}\mathrm{eV}$ electrons scattered by nitrogen trifluoride $({\mathrm{NF}}_{3})$ molecules have been measured using a linear transmission method under single collision conditions. It was found that the TCS energy function for ${\mathrm{NF}}_{3}$ is dominated with two pronounced enhancements: one resonantlike centered between 2 and $3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ with the maximum value of $28\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}$ followed with a minimum at around $7--12\phantom{\rule{0.3em}{0ex}}\mathrm{eV}(\ensuremath{\sim}17\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2})$, and the second much broader enhancement located around $40\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ ($19\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\phantom{\rule{0.3em}{0ex}}{\mathrm{m}}^{2}$ in the maximum). The low-energy enhancement is superimposed with some weak features located near 1.8, 2.2, and $2.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The integral elastic cross section has been calculated at intermediate energies using an independent atom method with a static plus polarization model potential. The cross section for ionization has been computed as well using the binary-encounter-Bethe approach. The sum of calculated cross sections reasonably reproduces the intermediate-energy experimental TCS, with respect to the shape and value. The TCS for ${\mathrm{NF}}_{3}$ is also compared with the TCS for ammonia $({\mathrm{NH}}_{3})$ which was supplementary measured and the effect of substitution of fluorine atoms for hydrogen (perfluorination effect) is demonstrated and discussed.