Electron Excitation Cross Sections Research Articles

Electron-driven molecular processes for cyanopolyacetylenes HC2n+1N (n = 3, 4, and 5).

Linear carbon series cyanopolyacetylenes (HC2n+1N) (n = 3, 4, and 5) are astromolecules found in the atmosphere of Titan and interstellar media such as TMC-1 (Taurus molecular cloud-1). All these compounds are also detected in IRC + 10 216. In the present work, we comprehensively investigate electron interaction with important cyanopolyacetylene compounds, viz. HC7N (cyano-tri-acetylene), HC9N (cyano-tetra-acetylene), and HC11N (cyano-penta-acetylene). The study covers incident electron energies ranging from the ionization threshold to 5 keV. Various electron-driven molecular processes are quantified in terms of total cross-sections. The quantum spherical complex optical potential (SCOP) is used to determine elastic (Qel) and inelastic (Qinel) cross-sections. Ionization is the most important inelastic effect that opens various chemical pathways for the generation of different molecular species; we computed the ionization cross-section (Qion) and discrete electronic excitation cross-section (ΣQexc) using the complex scattering potential-ionization contribution (CSP-ic) method. The cyanopolyacetylene compounds are difficult to handle experimentally owing to the health risks involved. Therefore, there are no prior experimental data available for these molecules; only Qion have been reported theoretically. Thus, the present work is the maiden report on computing Qel, Qinel, ΣQexc, and QT. In order to provide an alternative approach and further validation of the present work, we employed our recently developed two-parameter semi-empirical method (2p-SEM) to compute Qel and QT. Additionally, we predict the polarizability of the HC11N molecule, which has not been reported in the existing literature. This prediction is based on a correlation study of polarizabilities of molecules with Qion values from the same series of molecules.

Prediction of a complete and self-consistent collision cross-section set of C5F10O by data-driven method

The lack of a complete and consistent set of electron–molecule collision cross sections for the new eco-friendly gas C5F10O hinders the study of its microscopic discharge mechanisms. In this paper, we first calculate the elastic collision and electronic excitation cross-sections of C5F10O based on R-matrix theory and estimate its total attachment cross-sections through pulsed Townsend measurement. By combining cross sections from other literature, we are able to compile an initial set of collision cross-sections for C5F10O. However, this initial set remains incomplete and requires refinement. Therefore, this work establishes a neutral network to solve the inverse swarm problem of deriving cross-sections from swarm parameters. The inversion model is trained using a substantial amount of collision cross-sections from the LXCat project. Using the model and the initial set for C5F10O, a complete and self-consistent collision cross-section set for the C5F10O gas is predicted for the first time, based on the measured electron swarm parameters of C5F10O/Ar mixtures. The proposed method is capable of predicting C5F10O’s unknown vibrational excitation cross-section without any prior knowledge, thus enhancing its completeness. The refined set can reproduce the electron swarm parameters within an acceptable range of uncertainty, thus verifying its self-consistency. The set will be made available in the LXCat database, which is expected to be significant for fundamental studies of its discharge mechanisms as well as applications of C5F10O.

Calculations of positron scattering from small molecules

Recently, convergent close-coupling calculations have been completed for positron scattering from the carbon and oxygen atomic targets. These, together with previously completed calculations for atomic hydrogen, are utilized to perform positron scattering calculations for molecular hydrogen (H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {H}_2$$\\end{document}), molecular oxygen (O2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {O}_2$$\\end{document}), diatomic carbon (C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {C}_2$$\\end{document}), carbon monoxide (CO), carbon dioxide (CO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {CO}_2$$\\end{document}), ozone (O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {O}_3$$\\end{document}), water (H2O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {H}_2\\hbox {O}$$\\end{document}), and methane (CH4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {CH}_4$$\\end{document}) through a modified independent atom approach. For these molecules, positronium-formation, direct ionization, electron-loss, elastic, total electronic excitation, total inelastic, and total cross sections are obtained for energies between 0.1 and 5000 eV. There is, in general, good agreement between the current results and past experiments for most transitions, particularly at high energies where this approach is expected to be most accurate.Graphic

Dichotomy of the description of the elastic and electronically inelastic scattering of electrons by methane

The interaction between electrons and methane is studied with a particular focus on describing the dynamics of elastic and electronic excitation processes under the influence of the multichannel coupling effects. Elastic and electronically inelastic integral and differential cross sections are reported. These cross sections were calculated with the Schwinger multichannel method implemented with norm-conserving pseudopotentials within the minimal orbital basis for single-configuration interaction approach with up to 181 open channels. While an excellent agreement with previously published data is found in the elastic channel, the comparisons involving electronic excitation cross sections reveal significant discrepancies. Furthermore, the lack of reliable experimental data regarding the electronically inelastic channels hampers a more detailed analysis of the theoretical results. Additionally, total ionization and total cross sections for electron collisions with methane are also presented. By highlighting the current theoretical challenges in dealing with electron-induced electronic excitation of molecules, we seek to contribute to a deeper understanding of this scattering process and, thus, pave the way for future research.

Integral Electron Scattering Cross Sections from N2O for Impact Energies Ranging from 1 to 1000 eV.

Accurate total cross sections (TCS), within 5%, for electron scattering by N2O molecules have been measured with a magnetically confined electron transmission apparatus for impact energies ranging from 1 to 200 eV. For higher energies, these measurements have been complemented with our independent atom-based screening corrected additivity rule, including interference (IAM-SCAR + I) method to determine a complete reference TCS data set in the energy range (1-1000 eV). After a critical discussion that includes our calculated integral elastic and ionization cross sections and the theoretical and experimental data available in the literature, a complete set of integral elastic and inelastic (rotational, vibrational, and electronic excitation, ionization and electron attachment) cross sections, consistent with the reference TCS data, have been derived. This update on the N2O collisional database may help to improve the accuracy of radiation-induced transport models.

Theoretical study of a new molecular ion species BeN+: molecular states and cross sections for electronic excitation and dissociation.

We present here a theoretical study of a new molecular ion species BeN+, which has not been reported before. Using a good quality configuration interaction model, we first undertake a configuration interaction calculation of the molecular states to obtain the potential energy curves of several low lying states of BeN+ and the dipole and transition dipole moments of some of its states as a function of the internuclear distance. We find the ground state to be bound and of X 3Σ- character having a shallow minimum at Re = 2.9031a0 and several other closely spaced excited states some of which are repulsive. We have determined the spectroscopic parameters for some of these states by fitting the raw potential energy data to a 6-parameter analytical potential energy function. Subsequently, the R-matrix method is used to obtain electron collision cross sections for electronic excitation from the ground X 3Σ- state to several of its excited states at the equilibrium Re = 2.9031a0 and cross sections for electron impact dissociation. We have also reported many Feshbach resonances and their widths at the equilibrium Re = 2.9031a0, which may, in future studies, be extended to potential energy curves for neutral dissociative states. The states and cross sections obtained are of considerable significance for edge plasma chemistry in fusion devices operating with beryllium walls.

Elastic and electronically inelastic scattering of electrons by the pyrazine molecule.

We report on elastic and electronically inelastic integral and differential cross sections as well as ionization and total cross sections for electron collisions with the pyrazine molecule. The Schwinger multichannel method is applied in calculations carried out according to the minimal orbital basis for single configuration interactions strategy from the 1-channel up to 139-channels close-coupling level of approximation. With these calculations we have obtained integral and differential cross sections as well as excitation functions for elastic electron scattering and, also, integral and differential cross sections for electronic excitation from the ground state to the 3B1u, 3B2u, 3B3u, 1B1u, 1B2u and 1B3u excited states of pyrazine by electron impact. By summing the total ionization cross section obtained by means of the binary-encounter-Bethe model to these elastic and electronically inelastic contributions, we provided an estimate for the total cross section describing the electron-pyrazine interaction process. The independent atom model with the screening-corrected additivity rule plus interference terms method was also used in the present study to determine elastic integral and differential as well as ionization and total cross sections for electron collisions from pyrazine. The present results were, whenever possible, critically compared to the experimental and theoretical data available in the literature. In general, the overall agreement between the present results and the experiment is quite encouraging.

Low-energy inelastic electron scattering from carbon monoxide: Excitation and de-excitation of the X1Σ+, a3Π, a′3Σ+, A1Π, d3Δ, e3Σ−, I1Σ− and D1Δ electronic states

Cross-sections for electronic excitation and de-excitation among the ground state and lowest-lying seven electronic excited states of carbon monoxide (CO) by low-energy electron impact are computed using the R-matrix method. The excitation cross-sections from the ground state to the electronic states a3Π, a′3Σ+ and A1Π agree with previous experimental and theoretical results. In addition, the cross-sections for the I1Σ− and D1Δ states of CO, which will cascade to CO a′3Σ+ and A1Π states, are calculated. Furthermore, in contrast to the typical increase in electronic excitation cross-sections with collision energy, the de-excitation cross-sections show a negative trend with increasing energy.

Calculation of electronic excitation cross sections and rate coefficients for boron monohydride (BH)

Aiming at the quantitative diagnostics of boron monohydryde, BH, in fusion plasmas, we present elastic, electronic excitation, and ionization cross sections of BH for the first time. The calculations were performed by the R-matrix and Born Encounter Bethe methods utilized by Quantemol-EC software. To examine the uncertainty due to the calculation conditions, we compared the results by different basis sets and internuclear distances of the target model. We found that the uncertainties are typically within ∼10%. Rate coefficients were derived and fitted to an Arrhenius function. The derived decay rate per photon, , agreed with the value presented by Lieder et al (the ASDEX-Upgrade Team) (1994 Eur. Phys. Soc. Conf. Plasma Phys. 2 722).

Calculated cross sections for electron collisions with the BeN molecule

We report a low energy electron collision calculation with the BeN molecule in its X ground state using the molecular R-matrix method at a single geometry, namely, the equilibrium a 0 of the molecule. Using a suitable target model, we have calculated the elastic cross section and cross sections for electron impact excitation in several low-lying excited states of BeN. Cross sections for electron impact dissociation is derived from the electronic excitation cross sections. In addition, molecular data on bound sates of BeN and e-BeN negative ion resonances and widths at the target equilibrium Re that may be relevant for other studies are also provided.

Theoretical process for the investigation of dielectric characteristics of F3NO as an alternative gas for SF6

To examine the possibility of using a gas molecule as an SF6 alternative gas, the insulation properties of the molecule must be estimated. In this work, we present a theoretical approach to calculate geometry parameters, electron scattering cross sections, and transport properties of nitrogen fluoride oxide (F3NO), which we have selected as an alternative to SF6. The molecular minimum structure of F3NO was optimized using the ɷB97X-D functional combined with the aug-cc-pVTZ basis set. Using this initial geometry obtained by the molecular structure calculation, the R-matrix calculation was done to obtain the elastic and momentum transfer cross section. The BE-f method was used for electronic excitation cross section. For the ionization cross section, the binary encounter Bethe method was used. From the calculated cross section data, the electron transport coefficients and reaction coefficients were calculated by solving the two-term approximated Boltzmann equation to investigate the discharge and insulation characteristics.

Theoretical Investigation of Electron Impact Scattering on Imidazole.

This study presents the results of electron scattering calculations on a biologically important molecule, imidazole, using the UK molecular R-matrix method. The R-matrix calculations are performed using SE, SEP, and CC models, and the resonance detected in the present SEP model is found to be in better agreement with available experimental data than previous theoretical data. The study also reports an inelastic scattering cross section, which comprises dissociative electron attachment (DEA), excitation, and ionization cross section, for the first time. The total scattering cross sections are also reported for the first time. We confirm the presence of the two well-known π* shape resonances predicted earlier experimentally. Due to the scarcity of total scattering cross section (TCS) data for imidazole, we have compared the TCS of imidazole with its isoelectronic target isoxazole and drawn important conclusions. A comparison among the resonances of imidazole with those of isoxazole helps us to conclude that electron attachment to π* molecular orbitals is a general feature displayed by these five-membered heterocyclic compounds. The comprehensive electron scattering studies presented in this work are expected to provide a deeper understanding of electron-induced biochemical processes and fill gaps in the available data. Furthermore, this study is anticipated to inspire further investigations on imidazole and other five-membered heterocyclic ring molecules, which have significant applications in medicine.

Study of atomic spectroscopy and electron collision process in non-ideal classical plasmas

This manuscript presents an approach to the calculation of atomic properties and the electron collision excitation process in a non-ideal classical plasma, based on the relativistic distorted wave methodology. The method incorporating the pseudopotential obtained from a sequential solution of the Bogolyubov chain equations, that yields modification term to the calculation of the central field potential, is employed to characterize the interactions among the charged particles in plasmas. The bound/continuous state wave functions and the electron collision excitation matrix elements are determined using the aforementioned pseudopotential within a relativistic Dirac–Coulomb atomic structure framework. Systematic investigations on the effects of non-ideality of plasma on the electronic structures, radiative properties, and excitation cross sections within a selected temperature and density range are carried out in the specific cases of H atom and Ca18+ ion as they make it possible to reproduce the reference data well and thus to conclude with the reliability of the (present) method developed. Apart from its fundamental importance, this study is essential for several applications, especially for the analysis of atomic processes in non-ideal plasmas, and offers a new perspective for the calculation of atomic properties under different conditions in various astrophysical and laboratory plasmas.

Theoretical study of low-energy electron collision with normal-pentane using R-matrix method

Low-energy electron collisions with normal-pentane (n-C5H12) that initiate the plasma to assist combustion are critical in understanding the underlying physics and chemistries. In the present work, we studied this collisional process using the R-matrix method at the static-exchange plus polarization and close-coupling model levels. The scattering calculation was performed by running the UKRmol+ code using the Quantemol Electron Collision interface to obtain elastic differential, momentum transfer, integral, and electronic excitation cross sections up to 20 eV and ionization cross sections up to 1000 eV. Our computed cross-section data are in better agreement with the available experimental results both regarding the magnitude and shape. We also demonstrated the importance of using a diffuse basis set in describing the scattering due to the Rydberg nature of the lowest unoccupied molecular orbitals of n-C5H12.

Theoretical Study of Valence Shell Excitation by Electron Impact in CCl4

This paper reports a theoretical study of valence shell excitation in CCl4 by high-energy electron impact. Generalized oscillator strengths are calculated for the molecule at the equation-of-motion coupled-cluster singles and doubles level. To elucidate the influence of nuclear dynamics on electron excitation cross-sections, the effects of molecular vibration are included in the calculation. Based on a comparison with recent experimental data, several reassignments of spectral features are made, and it is found that excitations from the Cl 3p nonbonding orbitals to σ* antibonding orbitals, 7a1 and 8t2, play dominant roles below the excitation energy of ∼9 eV. Furthermore, the calculations reveal that distortion of the molecular structure due to the asymmetric stretching vibration significantly affects the valence excitations at small momentum transfers, where contributions from dipole transitions are dominant. It indicates that vibrational effects have a considerable influence on Cl formation in the photolysis of CCl4.

Elastic and inelastic low-energy electron scattering from pyridine.

A comprehensive investigation of elastic and inelastic electron scattering from molecular pyridine is reported using the ab initio R-matrix method with the static exchange plus polarization and close-coupling approximations for incident energies up to 10eV. The two well-known low-lying 1 2B1 and 1 2A2 shape resonances as well as a 2 2B1 mixed-character resonance compare well with the theoretical and experimental results. We also detect five core-excited resonances (1 2A1, 1 2B2, 3 2B1, 2 2A2, and 4 2B1), which lie above the first electronic excitation threshold. The total elastic cross sections and momentum transfer cross sections agree reasonably with previous reference data. Comparisons of the differential elastic cross sections of pyridine with those measured for benzene, pyrazine, and pyrimidine show remarkable agreement at scattering angles above 40° but behave differently for forward scattering below 40° below 6eV, due to the dominant effect of the permanent dipole moment on the differential cross section in the low energy region with narrow scattering angles. Inelastic electronic excitation cross sections are presented, showing the influence of core-excited resonances below the ionization threshold for the first time.

Theoretical study of low energy electron collisions with the BeO molecule

An R-matrix calculation is reported for low energy electron collision with the beryllium oxide (BeO) molecule at its equilibrium bond length a 0 for incident energies below 15 eV. Using a suitably constructed model to represent the BeO target, detailed scattering calculations are performed to obtain cross sections for many collision processes, namely total cross sections for elastic scattering and electronic excitations to some of its low lying states and cross section for electron impact dissociation. Additionally, we have also calculated differential cross sections for electronic excitations from the X ground state to the first two excited states of the target BeO molecule. BeO is likely to be present as an impurity component in the plasma of fusion devices operating with beryllium as first wall material. We therefore expect the present study to be of substantial importance to the fusion community.

Wave-packet continuum discretization approach to He2+−He collisions

The two-center wave-packet convergent close-coupling method is generalized to multiply charged ion collisions with helium and applied to the ${\mathrm{He}}^{2+}\text{\ensuremath{-}}\mathrm{He}$ scattering problem. The approach is applicable in a wide range of collision energies including low and intermediate energies, where coupling between various reaction channels and electron exchange between the fragments in the rearrangement channel are important. The target structure is treated using the configuration-interaction method within the frozen-core approximation, where one of the electrons of the target is assumed to stay in the ground state throughout the collision. This accounts for the indistinguishability and the correlations between the electrons of the target. We also use a simpler alternative method that is based on an effective one-electron target description that neglects the electron-electron correlations. In both methods, the continuum of the target atom and the hydrogenlike atom formed after electron capture by the projectile is discretized using the wave-packet approach. We present cross sections for total and state-selective electron capture, excitation, and single ionization of the target. The results are provided for the incident energies from 10 keV/u to 5 MeV/u, where one-electron processes are expected to dominate. Particular attention is focused on the intermediate-energy region where substantial deviations between various theoretical results are found. However, overall, the present results are in good agreement with experimental data and other calculations, where available. We demonstrate that both effective single-electron and two-electron methods can provide a realistic picture of all single-electron scattering processes taking place in ${\mathrm{He}}^{2+}\text{\ensuremath{-}}\mathrm{He}$ collisions in terms of the total cross sections. This creates a reliable platform for modeling differential scattering and ionization in this four-body system.

Extracting Inelastic Scattering Cross Sections for Finite and Aperiodic Materials from Electronic Dynamics Simulations.

Explicit time-dependent electronic structure theory methods are increasingly prevalent in the areas of condensed matter physics and quantum chemistry, with the broad-band optical absorptivity of molecular and small condensed-phase systems nowadays routinely studied with such approaches. In this paper, it is demonstrated that electronic dynamics simulations can similarly be employed to study cross sections for the scattering-induced electronic excitations probed in nonresonant inelastic X-ray scattering and momentum-resolved electron energy loss spectroscopies. A method is put forth for evaluating the electronic dynamic structure factor, which involves the application of a momentum boost-type perturbation and transformation of the resulting reciprocal space density fluctuations into the frequency domain. Good agreement is first demonstrated between the dynamic structure factor extracted from these electronic dynamics simulations and the corresponding transition matrix elements from linear response theory. The method is then applied to some extended (quasi)one-dimensional systems, for which the wave vector becomes a good quantum number in the thermodynamic limit. Finally, the dispersion of many-body excitations in a series of hydrogen-terminated graphene flakes (and twisted bilayers thereof) is investigated to highlight the utility of the presented approach for capturing morphology-dependent effects in the inelastic scattering cross sections of nanostructured and/or noncrystalline materials.

Electron impact inelastic molecular processes for deuterated compounds

In this theoretical work, electron induced inelastic molecular processes for deuterated molecules HD, D2, D2O, SiDx (x = 1–3), NDx (x = 1–3) and CDx (x = 2–4) are studied and quantified from ionisation threshold to 5 keV. The total inelastic cross section (Qinel) are computed using Spherical Complex Optical Potential (SCOP) and total ionisation cross sections (Qion) and total electronic excitation cross sections (∑Qexc) have been evaluated through the Complex Spherical Potential – ionisation contribution (CSP-ic) method. Electron driven inelastic effects for deuterated hydrogen (HD) are investigated for the first time in this study. This is the first report of total Qion for HD, SiDx (x = 1–3), NDx (x = 1,2), CDx (x = 2,3) molecules and maiden study of Qinel and ∑Qexc for all these molecules. Further, isotope effect is studied for these targets and using various correlation analyses, dipole polarizability for ND and SiDx (x = 1–3) molecules are predicted.