Total Electron Scattering Cross Sections Research Articles

Electron Scattering from 1-Methyl-5-Nitroimidazole: Cross-Sections for Modeling Electron Transport through Potential Radiosensitizers.

In this study, we present a complete set of electron scattering cross-sections from 1-Methyl-5-Nitroimidazole (1M5NI) molecules for impact energies ranging from 0.1 to 1000 eV. This information is relevant to evaluate the potential role of 1M5NI as a molecular radiosensitizers. The total electron scattering cross-sections (TCS) that we previously measured with a magnetically confined electron transmission apparatus were considered as the reference values for the present analysis. Elastic scattering cross-sections were calculated by means of two different schemes: The Schwinger multichannel (SMC) method for the lower energies (below 15 eV) and the independent atom model-based screening-corrected additivity rule with interferences (IAM-SCARI) for higher energies (above 15 eV). The latter was also applied to calculate the total ionization cross-sections, which were complemented with experimental values of the induced cationic fragmentation by electron impact. Double differential ionization cross-sections were measured with a reaction microscope multi-particle coincidence spectrometer. Using a momentum imaging spectrometer, direct measurements of the anion fragment yields and kinetic energies by the dissociative electron attachment are also presented. Cross-sections for the other inelastic channels were derived with a self-consistent procedure by sampling their values at a given energy to ensure that the sum of the cross-sections of all the scattering processes available at that energy coincides with the corresponding TCS. This cross-section data set is ready to be used for modelling electron-induced radiation damage at the molecular level to biologically relevant media containing 1M5NI as a potential radiosensitizer. Nonetheless, a proper evaluation of its radiosensitizing effects would require further radiobiological experiments.

Electron and Positron Scattering Cross Sections from CO2: A Comparative Study over a Broad Energy Range (0.1–5000 eV)

In this Review, we present a comparative study between electron and positron scattering cross sections from CO2 molecules over a broad impact energy range (0.1–5000 eV). For electron scattering, new total electron scattering cross sections (e-TCS) have been measured with a high resolution magnetically confined electron beam transmission system from 1 to 200 eV. Dissociative electron attachment processes for electron energies from 3 to 52 eV have been analyzed by measuring the relative O– anion production yield. In addition, elastic, inelastic, and total scattering cross section calculations have been carried out in the framework of the Independent Atom Model by using the Screening Corrected Additive Rule, including interference effects (IAM-SCARI). Based on the previous cross section compilation from Itikawa (J. Phys. Chem. Ref. Data, 2002, 31, 749−767) and the present measurements and calculations, an updated recommended e-TCS data set has been used as reference values to obtain a self-consistent integral cross section data set for the elastic and inelastic (vibrational excitation, electronic excitation, and ionization) scattering channels. A similar calculation has been carried out for positrons, which shows important differences between the electron scattering behavior: e.g., more relevance of the target polarization at the lower energies, more efficient excitation of the target at intermediate energies, but a lower total scattering cross section for increasing energies, even at 5000 eV. This result does not agree with the charge independence of the scattering cross section predicted by the first Born approximation (FBA). However, we have shown that the inelastic channels follow the FBA’s predictions for energies above 500 eV while the elastic part, due to the different signs of the scattering potential constituent terms, remains lower for positrons even at the maximum impact energy considered here (5000 eV). As in the case of electrons, a self-consistent set of integral positron scattering cross sections, including elastic and inelastic (vibrational excitation, electronic excitation, positronium formation, and ionization) channels is provided. Again, to derive these data, positron scattering total cross sections based on a previous compilation from Brunger et al. (J. Phys. Chem. Ref. Data, 2017, 46, 023102) and the present calculation have been used as reference values. Data for the main inelastic channels, i.e. direct ionization and positronium formation, derived with this procedure, show excellent agreement with the experimental results available in the literature. Inconsistencies found between different model potential calculations, both for the elastic and inelastic collision processes, suggest that new calculations using more sophisticated methods are required.

A complete data set for the simulation of electron transport through gaseous tetrahydrofuran in the energy range 1\u2013100 hbox {eV}

A self-consistent data set, with all the necessary inputs for Monte Carlo simulations of electron transport through gaseous tetrahydrofuran (THF) in the energy range 1–100 eV, has been critically compiled in this study. Accurate measurements of total electron scattering cross sections (TCSs) from THF have been obtained, and considered as reference values to validate the self-consistency of the proposed data set. Monte Carlo simulations of the magnetically confined electron transport through a gas cell containing THF for different beam energies (3, 10 and 70 eV) and pressures (2.5 and 5.0 mTorr) have also been performed by using a novel code developed in Madrid. In order to probe the accuracy of the proposed data set, the simulated results have been compared with the corresponding experimental data, the latter obtained with the same experimental configuration where the TCSs have been measured.Graphic

Electron scattering cross sections from nitrobenzene in the energy range 0.4-1000 eV: the role of dipole interactions in measurements and calculations.

Absolute total electron scattering cross sections (TCS) for nitrobenzene molecules with impact energies from 0.4 to 1000 eV have been measured by means of two different electron-transmission experimental arrangements. For the lower energies (0.4-250 eV) a magnetically confined electron beam system has been used, while for energies above 100 eV a linear beam transmission technique with high angular resolution allowed accurate measurements up to 1000 eV impact energy. In both cases random uncertainties were maintained below 5-8%. Systematic errors arising from the angular and energy resolution limits of each apparatus are analysed in detail and quantified with the help of our theoretical calculations. Differential elastic and integral elastic, excitation and ionisation as well as momentum transfer cross sections have been calculated, for the whole energy range considered here, by using an independent atom model in combination with the screening corrected additivity rule method including interference effects (IAM-SCARI). Due to the significant permanent dipole moment of nitrobenzene, additional differential and integral rotational excitation cross sections have been calculated in the framework of the Born approximation. If we ignore the rotational excitations, our calculated total cross section agrees well with our experimental results for impact energies above 15 eV. Additionally, they overlap at 10 eV with the low energy Schwinger Multichannel method with Pseudo Potentials (SMCPP) calculation available in the literature (L. S. Maioli and M. H. F. Bettega, J. Chem. Phys., 2017, 147, 164305). We find a broad feature in the experimental TCS at around 1.0 eV, which has been related to the formation of the NO2- anion and assigned to the π*(b1) resonance, according to previous mass spectra available in the literature. Other local maxima in the TCSs are found at 4.0 ± 0.2 and 5.0 ± 0.2 eV and are assigned to core excited resonances leading to the formation of the NO2- and O2- anions, respectively. Finally, for energies below 10 eV, differences found between the present measurements, the SMCPP calculation and our previous data for non-polar benzene have revealed the importance of accurately calculating the rotational excitation contribution to the TCS before comparing theoretical and experimental data. This comparison suggests that our dipole-Born calculation for nitrobenzene overestimates the magnitude of the rotational excitation cross sections below 10 eV.

New magnetized electron beam apparatus and measurement of total electron scattering cross section of N2O at intermediate energy region

SynopsisA new electron scattering apparatus is developed based on concepts from the positron system built by Surko et al. In an electron-version of the system, the electron beam is provided by a cathode and the rest of the system is correspondingly modified to a simpler system. The system was tested with argon to verify its operation. N2O is important in atmosphere and plasma, and in the intermediate energy region, there are two previous results which are in disagreement. We present here a result for the total electron cross section of N2O.

Experimental and theoretical analysis for total electron scattering cross sections of benzene.

Measurements of the total electron scattering cross sections (TCSs) from benzene, in the impact energy range of 1-1000 eV, are presented here by combining two different experimental systems. The first utilizes a magnetically confined electron transmission beam for the lower energies (1-300 eV), while the second utilizes a linear transmission beam apparatus for the higher energies (100-1000 eV). These cross sections have also been calculated by means of two different theoretical methods, the Schwinger Multichannel with Pseudo Potential (SMCPP) procedure, employing two different approaches to account for the polarization of the target for impact energies between 0.1 and 15 eV, and the Independent Atom Model with the Screening Corrected Additivity Rule including Interference effect (IAM-SCAR+I) paradigm to cover the 10-10 000 eV impact energy range. The present results are compared with available theoretical and experimental data, with the level of accord being good in some cases and less satisfactory in others, and some predicted resonances have been identified. In particular, we found a π* shape resonance at 1.4 eV and another feature in the energy region 4.6-4.9 eV interpreted as a π* resonance (2B2g symmetry), which is a mixture of shape and a core excited resonance, as well as a Feshbach resonance at 5.87 eV associated with the 3s (a1g) Rydberg state. A Born-type formula to extrapolate TCS values for energies above 10 000 eV is also given. This study provides a complete set of TCS data, with uncertainty limits within 10%, ready to be used for modeling electron transport applications.

Total electron scattering cross sections from thiophene for the (1-300 eV) impact energy range.

Experimental electron scattering cross sections for thiophene in the impact energy range from 1 to 300 eV have been measured with a magnetically confined electron transmission-beam apparatus. Random uncertainty limits have been estimated to be less than 5%, and systematic errors derived from acceptance angle limitations have also been identified and evaluated. Experimental values are compared with our previous low energy (1-15 eV) R-matrix and intermediate/high energy (15-300 eV) IAM-SCAR+I calculations finding reasonable agreement, within the combined uncertainty limits. Some of the low energy shape and core-excited resonances predicted by previous calculations are experimentally confirmed in this study.

Total electron-scattering cross sections from pyridine molecules in the energy range 1–200 eV

Total electron-scattering cross sections from pyridine molecules in the energy range 1–200 eV

Total electron scattering cross section from sevoflurane by 1–300 eV energy electron impact

We report on novel total electron scattering cross section (TCS) measurements for electrons scattering from sevoflurane, at incident electron impact energies in the range 1–300 eV. The experimental results, obtained from a newly implemented magnetic beam apparatus based in Madrid, are compared with theoretical results from the independent atom model with screening corrected additivity rule including interference effects and rotational excitation (IAM-SCAR+I+R). A very good level of agreement has been found between the present experimental and theoretical data at above about 20 eV electron impact and to within the experimental uncertainties.

Total electron scattering cross section from pyridine molecules in the energy range 10–1000 eV

We report on experimental total electron scattering cross-section (TCS) from pyridine (C5H5N) for incident electron energies between 10 and 1000 eV, with experimental uncertainties within 5–10%, as measured with a double electrostatic analyser apparatus. The experimental results are compared with our theoretical calculations performed within the independent atom model complemented with a screening corrected additivity rule (IAM-SCAR) procedure which has been updated by including interference effects. A good level of agreement is found between both data sources within the experimental uncertainties. The present TCS results for electron impact energy under study contribute, together with other scattering data available in the literature, to achieve a consistent set of cross section data for modelling purposes.

Total electron scattering cross sections from para-benzoquinone in the energy range 1-200 eV.

Total electron scattering cross sections, from para-benzoquinone, for impact energies ranging between 1 to 200 eV, have been obtained by measuring the attenuation of a linear electron beam under magnetic confinement conditions. Random uncertainty limits on these values have been found to be within 5%. Systematic errors, due to the axial magnetic beam conditions in combination with the acceptance angle of the detector, have been evaluated by integrating our calculated independent atom model with the screening corrected additivity rule and interference term elastic differential cross sections over that detection acceptance angle. Our previous calculations and measurements on this molecule (Jones et al., J. Chem. Phys., 2018, 148, 124312 and J. Chem. Phys., 2018, 148, 204305), have been compiled and complemented with new elastic and inelastic scattering cross section calculations in order to obtain a comprehensive cross section data base, within the considered energy range, for modelling purposes. The self-consistency of the present data set has been evaluated by simulating the electron transport of 15 eV electrons in para-benzoquinone, and comparing those results with the observed transmitted intensity distribution.

The interaction of low-energy electrons with fructose molecules

Using a hypocycloidal electronic spectrometer, the interactions of low energy electrons (0–8.50 eV) with fructose molecules, namely, electron scattering and dissociative attachment, are studied. The results of these studies showed that the fragmentation of fructose molecules occurs effectively even at an electron energy close to zero. In the total electron-scattering cross section by molecules, resonance features (at energies ~3.10 and ~5.00 eV) were first observed near the formation thresholds of light ion fragments OH– and H–. The correlation of the features observed in the cross sections of electron scattering and dissociative attachment is analyzed.

Total cross section of furfural by electron impact: Experiment and theory

We present experimental total cross sections for electron scattering from furfural in the energy range from 10 to 1000 eV, as measured using a double electrostatic analyzer gas cell electron transmission experiment. These results are compared to theoretical data for furfural, as well as to experimental and theoretical values for the structurally similar molecules furan and tetrahydrofuran. The measured total cross section is in agreement with the theoretical results obtained by means of the independent-atom model with screening corrected additivity rule including interference method. In the region of higher electron energies, from 500 eV to 10 keV, the total electron scattering cross section is also estimated using a semi-empirical model based on the number of electrons and dipole polarizabilities of the molecular targets. Together with the recently measured differential and integral cross sections, and the furfural energy-loss spectra, the present total cross section data nearly complete the data set that is required for numerical simulation of low-energy electron processes in furfural, covering the range of projectile energies from a few electron volts up to 10 keV.

Total electron scattering cross sections of some important biomolecules at 0.2–6.0 keV energies

The total electron scattering cross sections (TCS) of five nucleic bases (adenine, cytosine, guanine, thymine and uracil), phosphoric acid, three amino acids (glycine, lysine, and l-histidine), d-glucose, alpha-d-glucose, tetrahydropyran (THP), 3-hydroxytetrahydrofuran and furan have been determined in the energy range 0.2–6.0keV using a simple model based on the effective atomic total electron scattering cross sections (EATCS). The reliability of the model is confirmed by comparing the determined TCS with the predictions of those by existing theoretical models.

Total electron scattering cross sections of molecules containing H, C, N, O and F in the energy range 0.2–6.0 keV

Based on the effective atomic total electron scattering cross sections (EATCS) of atoms in a molecular environment, a simple model is proposed to predict the total electron scattering cross sections (TCS) of H, C, N, O, and F containing molecules. The EATCS for these five atoms are reported for 0.2–6.0keV energies. The predicted TCS by this model are compared with experimental TCS in the literature. The experimental TCS of CHF3, C2F4, C2F2H2, C4F6, and c-C4F8 have been obtained for 0.2–4.5keV electrons by measuring the attenuation of the electron beam through a gas cell.

Electron-scattering cross sections for selected alkyne molecules: Measurements and calculations

We report cross-section results from experimental and theoretical studies on electron collisions with 1-butyne ($\text{HC}\ensuremath{\equiv}\text{C}--{\text{CH}}_{2}{\text{CH}}_{3}$) and acetylene ($\text{HC}\ensuremath{\equiv}\text{CH}$) molecules and from computations for a propyne ($\text{HC}\ensuremath{\equiv}\text{C}--{\text{CH}}_{3}$) molecule. Absolute $grand\phantom{\rule{0.16em}{0ex}}$-total electron-scattering cross sections (TCSs) were measured at impact energies ranging from about 0.5 to 300 eV using the linear electron-transmission method. The TCS energy curve for 1-butyne has a very broad enhancement on which some distinct features are superimposed, namely a resonant-like maximum (located near 3.2 eV), a broad hump (centered around 7.5 eV), and a shoulder (spanned between 12 and 26 eV). The shape of our experimental TCS curve for acetylene closely resembles that reported earlier, while its magnitude is usually larger. As no previous calculations for electron collisions with 1-butyne and propyne are disclosed in the literature, we computed the elastic (ECS) and ionization (ICS) cross sections for these molecules. Similar calculations were also performed for acetylene molecules. The additivity rule was employed to calculate the ECSs from 50 to 3000 eV, while the binary-encounter-Bethe approach was used for computation of the ICSs, from the threshold up to 3000 eV. The sum (ECS + ICS) of these two computed cross sections reasonably reproduces the TCS measurements above 50 eV. Furthermore, the experimental TCS curves, obtained in our laboratory, for a series of acetylenic compounds---acetylene ($\text{HC}\ensuremath{\equiv}\text{CH}$), propyne ($\text{HC}\ensuremath{\equiv}\text{C}--{CH}_{3}$), and 1-butyne ($\text{HC}\ensuremath{\equiv}\text{C}--{\text{CH}}_{2}{\text{CH}}_{3}$)---are compared to study the substitutional effect. Finally, the influence of the structural differences on the electron-scattering TCS for isomers of the ${\text{C}}_{4}{\text{H}}_{6}$ molecule (1-butyne, 2-butyne, and 1,3--butadiene) is indicated and discussed.

Total electron scattering cross sections for pyrimidine and pyrazine as measured using a magnetically confined experimental system

In this paper, a recently constructed apparatus for measuring electron scattering cross sections while applying a strong axial magnetic field is utilized for determining total scattering cross sections. The first molecules studied with this setup are pyrimidine (1,3-diazine) and pyrazine (1,4-diazine), whose total cross sections are obtained for the incident electron energy range of 8-500 eV. Quite good agreement with earlier theoretical predictions is found after accounting for the angular acceptance (angular resolution for forward scattering) of the apparatus. However, no other experimental total cross sections for electron scattering from pyrimidine or pyrazine have been found in the literature for comparison.

An investigation into electron scattering from pyrazine at intermediate and high energies

Total electron scattering cross sections for pyrazine in the energy range 10-500 eV have been measured with a new magnetically confined electron transmission-beam apparatus. Theoretical differential and integral elastic, as well as integral inelastic, cross sections have been calculated by means of a screening-corrected form of the independent-atom representation (IAM-SCAR) from 10 to 1000 eV incident electron energies. The present experimental and theoretical total cross sections show a good level of agreement, to within 10%, in the overlapping energy range. Consistency of these results with previous calculations (i.e., the R-matrix and Schwinger Multichannel methods) and elastic scattering measurements at lower energies, below 10 eV, is also discussed.

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

In this paper, an apparatus for measuring electron-scattering cross sections while applying a strong axial magnetic field is described. The first original experiment performed with this setup is the measurement of the total cross sections for pyrimidine (1,3-diazine), which are presented for the incident electron energy range of 8--500 eV. Generally good agreement with earlier theoretical predictions is found after accounting for the angular acceptance (angular resolution for forward scattering) of the apparatus.

Total electron-scattering cross sections of pyrimidine

Total electron-scattering cross sections of pyrimidine, the basic component for the nucleic bases cytosine and thymine, were measured for electron energies from 5 eV to 1 keV using the linear transmission method. The measured results were compared to semiempirical data obtained by means of the additivity rule and to experimental data for benzene since it has a similar ring structure and the same number of valence electrons as pyrimidine. Furthermore, integral elastic and inelastic electron-scattering cross sections of pyrimidine were calculated by applying the spherical complex optical potential model. The sum of both cross sections agrees reasonably well with the experimental total electron-scattering cross sections of pyrimidine in the energy range from 20 eV to 1 keV. The experimental data are, however, significantly lower than the theoretical cross sections when including the contribution of rotational excitations to the electron scattering.