Electron-impact Cross Sections Research Articles

Electron impact cross-sections of tetraethyl silicate

Understanding the interactions of electrons with molecules in plasma is of vital importance from both academic and technological points of view. Reliable electron collision data is required to model the electron and ion components of low-temperature and nonequilibrium plasmas. Various electron impact cross sections such as the differential, integral, momentum transfer, partial and total ionizations are reported for tetraethyl silicate (TEOS), a plasma-relevant molecule in the energy range between the ionization threshold and 5 keV. The elastic (differential, integral and momentum transfer) cross sections are obtained by invoking the molecular approach and local potential approximation within the single center expansion formalism. The dissociative ionization cross sections are reported within the binary encounter Bethe (BEB) model formalism. The elastic and ionization cross sections are summed incoherently to estimate total cross sections. A good agreement is observed between the present results and others that are available. This work validates the efficacy of the modified BEB model in computing the partial ionization cross sections.

Experimental method for determination of the integral cross-section for electron impact ionization of ions with optical control of the target’s initial quantum state

A method for measurement of integral cross-sections for electron impact ionization of ions is proposed. The technique involves the application of a quadrupole ion trap with laser-cooled ions. It allows controlling the initial quantum state of the target ions, measuring the cross-sections separately for such states. The methodology is described in detail, together with a discussion of the reliability of optical selection of the ions’ states. The first results for Ca+ ion ionization from 42S1/2 and 32D3/2 states are presented.

Low-temperature plasma simulation based on physics-informed neural networks: Frameworks and preliminary applications

Plasma simulation is an important, and sometimes the only, approach to investigating plasma behavior. In this work, we propose two general artificial-intelligence-driven frameworks for low-temperature plasma simulation: Coefficient-Subnet Physics-Informed Neural Network (CS-PINN) and Runge–Kutta Physics-Informed Neural Network (RK-PINN). CS-PINN uses either a neural network or an interpolation function (e.g., spline function) as the subnet to approximate solution-dependent coefficients (e.g., electron-impact cross sections, thermodynamic properties, transport coefficients, etc.) in plasma equations. Based on this, RK-PINN incorporates the implicit Runge–Kutta formalism in neural networks to achieve a large-time step prediction of transient plasmas. Both CS-PINN and RK-PINN learn the complex non-linear relationship mapping from spatiotemporal space to the equation's solution. Based on these two frameworks, we demonstrate preliminary applications in four cases covering plasma kinetic and fluid modeling. The results verify that both CS-PINN and RK-PINN have good performance in solving plasma equations. Moreover, RK-PINN has the ability to yield a good solution for transient plasma simulation with not only large time steps but also limited noisy sensing data.

Ionospheric photoelectrons: A lateral thinking approach

This paper presents a personal account of developments in the solution of two related problems that limited the accuracy of ionosphere calculations in the 1980s. The first problem concerns the model-data discrepancies in the ionosphere photoelectron flux spectrum. Early comparisons between measured and modeled data revealed discrepancies in magnitude and shape. A lateral thinking approach revealed that there were problems with two key photoelectron model inputs: namely, the electron impact cross-sections and the solar extreme ultraviolet irradiance. This work led to the development of a widely used EUVAC solar irradiance model for ionosphere electron density calculations. The second problem relates to the neutral winds that are crucial for modeling variations in the ionosphere ion and electron densities. There is a lack of thermosphere neutral wind data because they are difficult to measure. The winds determine the altitude at which the electron density peaks. An accurate solution to this problem was the development of an algorithm that assimilates the altitude of the peak electron density into ionosphere models. This technique works because the altitude of the peak density is very sensitive to variations in the neutral wind.

Mass Spectrometry-Based Approach to Compute Electron-Impact Partial Ionization Cross-Sections of Methane, Water and Nitromethane from Threshold to 5 keV

The electron impact partial ionization cross-sections of molecules such as methane, water and nitromethane are computed using a modified form of the binary encounter Bethe (BEB) formula. The modified form of the BEB model works on rescaling the molecular binding energies of the orbitals and the scaling of cross-sections using the electron ionization mass spectrometry data. The computed partial ionization cross-sections are consistent with the recommended data and are better than several experimental and theoretical results. The summed partial ionization cross-sections of different fragments also agree with the total ionization cross-sections obtained from BEB and the experimental data. This work highlights the utility of mass spectrometry in the modeling and interpretation of the ionization cross-section data. The limitations and the advantages of the modified form of the BEB model are also discussed.

Electron-impact ionization cross sections of small molecules containing Fe and Cr ∗ ∗ This work is dedicated to Enrico Clementi who pioneered the interdisciplinary use of quantum chemistry and computational modelling.

We present the electron-impact ionization cross sections (EICSs) of iron and chromium hydrides, nitrides, and oxides. The motivation of this work stems from the fact that chemical sputtering from a steel surface exposed to a hot plasma can create these molecules which in turn influence the composition and energy balance of the plasma. The latter influence is quantified by the EICS which we derive by using two semi-empirical methods which can be employed in the relevant energy range of 10–1000 eV. They are important molecular properties for plasma- and materials science. We discuss the foundations of the methods and present the cross sections of the high- and low-spin states of the species in their neutral ground states and of their cations.

Confined helium, density dependence of the inelastic electron and photon scattering cross-sections and the optical oscillator strength

The electron and photon excitation of confined and compressed atoms is discussed. It is shown that the optical oscillator strength, the inelastic X-ray and electron impact cross-sections are all density-dependent. Ab-initio electronic structure calculations are presented for the 1 s 2 → 1 s 2 p ( 1 P ) transition in helium, which predict that the amplitudes for the inelastic scattering of electrons, optical absorption and the excitation energy are all significantly increased in bulk condensed phases of pure helium compared to those of an isolated atom. The enhancements increase with atomic density but are very similar for bcc and fcc structured bulk phases of the same density. These enhancements need to be incorporated into the analysis of scanning transmission electron microscope studies of helium nano bubbles embedded in different materials. The excitation energy and cross-section enhancements with increasing density arise from the contraction of the 2 p orbital on entering a condensed phase. For the bulk phases, but not the bubbles, the close agreement between the experimental and computed values of the energy shifts can be well described by a simple relationship.

Vibrational excitation cross sections for non-equilibrium nitric oxide-containing plasma

A full set of vibrationally-resolved cross sections for electron impact excitation of NO(X2Π, v) molecules is calculated from ab initio molecular dynamics, in the framework of the local-complex-potential approach. Electron–vibration energy exchanges in non-equilibrium thermodynamic conditions are studied from a state-to-state model accounting for all electron impact excitation and de-excitation processes of the nitric oxide vibration manifold, and it is shown that the calculated vibration relaxation times are in good agreement with the experimental data. The new vibrational excitation cross sections are used in a complete electron impact cross section set in order to obtain non-equilibrium electron energy distributions functions and to calculate electron transport parameters in NO. It is verified that the new cross sections bring a significant improvement between simulations and experimental swarm data, providing an additional validation of the calculations, when used within the complete set of cross sections investigated in this work.

Electron-impact cross sections of acetylene up to 5 keV

Electron-impact cross sections of acetylene up to 5 keV

Total Ionization Cross Sections due to Electron Impact of Carbon Tetrafluoride from Ionization Threshold to 10 MeV

Modified Khare-BEB model has been used to calculate the electron impact ionization cross section for carbon tetrafluoride (CF4) from ionization threshold to 10 MeV. The collisional parameters CRP and also has been calculated. The calculations are compared with available experimental data . A good agreement is found among the present results, other previous calculations, and experimental data.

Contribution of the metastable states to electron-impact single ionization for W7+

In this paper, we present the electron-impact single ionization cross sections for W7+. The level-to-level distorted-wave method implemented in the flexible atomic code (FAC) was used for calculation. Contributions from direct ionization (DI) and excitation-autoionization (EA) processes are taken into account. Comparison between the results of previous experimental measurements and the present calculations show a prominent contribution from metastable states in the W7+ ion. We extended the theoretical analysis including level-to-level calculations from long-lived levels of the [Cd]4f135p6 ground configuration and excited, metastable [Cd]4f145p5, [Cd]4f135p55d and [Cd]4f145p45d configurations. Calculated results are in good agreement with experimental data when, within a statistical model, a 56% fraction of parent ions in the ground configuration is assumed.

A binary-encounter-Bethe approach to compute electron-impact partial ionization cross sections of plasma relevant molecules such as hexamethyldisiloxane and silane

Electron-impact partial ionization cross sections (PICS) of fragments are reported from threshold to 5 keV energy using a modified form of the binary-encounter-Bethe model. Scaling using mass spectrometry data ensures that the cross sections are of the correct order of magnitude. The total ionization cross sections (TICS) were obtained by summing the PICS of fragments. The PICS and TICS obtained from the modified-binary-encounter-Bethe model are in excellent agreement with the experimental and theoretical results. The molecules investigated are hexamethyldisiloxane and silane. Both these species are highly relevant in plasma processing where the PICS are required to be over an extended energy range. The study of the ionization process in conjunction with mass spectrometry provides correct estimates of the contribution that each charged ion makes to the TICS. The present approach can be easily extended to any species provided that ion energetics and relative cation abundances data are available.

Structural, spectroscopic and electron collisional studies of isoxazole (C3H3NO)

• Comprehensive structural, spectroscopic and electron collision data of Isoxazole. • DFT calculations of ground state geometry and vibrational frequencies. • Comparison with earlier data; confirmation/revision of vibronic assignments. • Vertical excitation energies for singlet and triplet states using TDDFT. • Low energy electron scattering data for Isoxazole from 0.1-20 eV. The structural, spectroscopic, and electron collision data of Isoxazole (C 3 H 3 NO) were subjected to extensive computational studies. Spectroscopic calculations were performed on ground and excited states using the density functional theory (DFT) and the time dependent density functional theory (TDDFT) respectively. Ground state geometry and vibrational frequencies agree well with earlier works and lead to re-assignment of a few vibrational bands. Theoretically predicted singlet and triplet excitation energies are in good agreement with earlier experimental data, while predicted oscillator strengths of singlet states correlate well with the observed relative spectral intensities. The electron collision data for isoxazole molecule were calculated using Quantemol-N, which employs the UK Molecular R-matrix codes. These calculations were performed for the total elastic cross-sections along with their symmetrical components, differential and momentum transfer cross-sections, inelastic scattering cross-sections comprising of discrete electronic excitation, ionization and dissociative electron attachment processes. We employed the two most popular theoretical approaches to calculate the electron impact ionization cross-sections viz. Complex scattering potential-ionization contribution (CSP-ic) and the Binary encounter Bethe (BEB) model. The rate coefficients for elastic and inelastic processes were estimated over a wide electron temperature range. In addition to scattering calculations, the other motivation was to obtain resonances which are signatures of many significant low energy phenomena. The first two peak correspond to π* shape resonances which are observed at 2.1 eV and 4.69 eV and are in accordance with the earlier reported data. The third peak is observed at 10.96 eV which may be attributed to the σ* shape resonance.

Study of Electron Impact Ionization Cross-Sections of Nitrogen Molecule by Inelastic Collision

In this article, the calculation of ionization cross-section of N2 molecule by electron impact is reviewed. The work on ionization cross-sections from threshold to high (10 KeV) incident electron energies are calculated and their applications are discussed. To find exact values of total ionization cross-sections for the N2 molecule, a semiempirical approach of Jain and Khare (1976) is adopted which is a modification to eliminate the error factors, and then it is compared with the existing experimental and/or theoretical data which gives satisfactory results

Calculated electron impact ionisation fragmentation patterns

There are many measurements and calculations of total electron impact ionisation cross sections. However, many applications, particularly in plasma physics, also require fragmentation patterns. Approximate methods of deducing partial cross sections are tested based on the use of total cross section computed within the well-used binary encounter Bethe approximation. Partial ionisation cross sections for three series of molecules including CH4, CF4 and CCl4; SiH4 and SiCl4; NH3 and PH3, were estimated using two methods. Method one is semi-empirical and uses mass spectroscopy data to fix the partial cross sections at a single electron energy. The second is a fully computational method proposed by Huber et al (2019 J. Chem. Phys. 150 024306). Comparisons with experimental results suggest that the mass spectroscopy method is more accurate. However, as Huber’s method requires no experimental input, this method could be used as a first approximation when no experimental data is available. As mass spectroscopy sometimes provides incomplete datasets, a hybrid method based on the use of both methods is also explored.

Thermospheric Composition and Solar EUV Flux From the Global‐Scale Observations of the Limb and Disk (GOLD) Mission

AbstractObservations of far‐ultraviolet (FUV) dayglow by the Global‐scale Observations of Limb and Disk (GOLD) mission provide a new opportunity to monitor relative composition changes in the upper atmosphere as well as solar extreme ultraviolet (EUV) variability. Relative composition changes are quantified by ΣO/N2, the column density ratio of atomic oxygen to molecular nitrogen, while QEUV provides a measure of the solar EUV energy flux from 1 to 45 nm into the upper atmosphere. This spectral range provides the ionizing radiation which ultimately results in FUV airglow emission produced by photodissociation and photoelectron impact. The quantities ΣO/N2 and QEUV are derived from GOLD FUV observations through lookup tables that are constructed using a first‐principles photoelectron transport model. The two FUV emissions used are O I 135.6 nm and the N2 Lyman‐Birge‐Hopfield (LBH) bands. We present an overview of the theoretical basis for the algorithms and practical considerations for application to GOLD data. The effects of uncertainties in electron impact cross sections, off‐nadir viewing, and instrument artifacts are reviewed. We also discuss GOLD Level 1C DAY, Level 2 data products ON2 and QEUV, and present representative samples of each.

Electron-impact ionization of Ar2+

We study electron-impact single-ionization cross-sections for all levels of the ground configuration of the Ar2+ ion using the distorted wave approximation. We investigate the influences of the direct ionization and excitation-autoionization processes on the total single-ionization cross sections. We used corrected energies for the levels of the Ar3+ ion so that the ionization threshold corresponds to the value recommended by National Institute of Standards and Technology (NIST). Radiative damping is taken into account for the ionization cross-sections of the indirect process. Excitations from the 3s and 3p subshells are investigated for the indirect process. We demonstrate that the excitations from the outermost 3p subshell of the ground configuration provide an important contribution to the single ionization cross-sections at low energies. Fairly good agreement with measurements is obtained for the ground level of the Ar2+ ion. We show that the direct ionization provides ~70% at peak of the total single-ionization cross-sections.

Development of various methods to the investigation of the spectral properties and collision dynamics of H‐like ions taking place in dense and hot plasma environments

AbstractThe correct understanding of the behavior of highly stripped ions immersed in a dense plasma environment is a hitherto challenge for theory and it is of importance in various applications. Here, we developed four kinds of novel theoretical models to the determination of the spectral properties and collision dynamics of H‐like ions in dense and hot plasmas by employing the analytical potential [Li et al., Phys. Plasmas 2019, 26, 033301] to describe the interactions among the charged particles: (i) The electron photon processes in plasma model within the relativistic scheme; (ii) The multiconfiguration Dirac–Fock model within the framework of relativistic self‐consistent iteration approximation; (iii) The generalized pseudospectral method within the relativistic framework; and (iv) An analytic formula based on the Hartree–Fock method and the irreducible tensor theory within the non‐relativistic regime, derived from a solution of Schrödinger equation. As a typical example, energy eigenvalues, radiative transition properties, spectral line shifts, and electron impact excitation and ionization cross sections of the selected N6+ and Ne9+ ions are determined for several temperature‐density cases, characteristic of inertial confinement fusion plasmas. A comparison of these results with each other and the results from earlier calculations as well as with the available experimental data is provided. Systematic trend is determined for all the properties under study concerning increased screening. The present study not only extends our understanding of the dense plasma shielding effects, but also opens the way for future investigations allowing accurate predictions of spectral properties of ions in dense and hot plasmas aimed at providing precision data for various practical applications.

Non-dissociative ionization cross section of the electronically excited H2 and D2 with atomic-limit principal quantum number n[formula omitted] 3 and 4

Electron-impact cross sections for non-dissociative ionization via the ground vibrational level (v=0) of the electronically excited H2 and D2 with atomic-limit principal quantum number n= 3–4, including HH¯1Σg+, B′1Σu+, D1Πu, GK1Σg+, I1Πg, J1Δg, O1Σg+, B′′B¯1Σu+, D′1Πu, P1Σg+, R1Πg, S1Δg, h3Σg+, e3Σu+, d3Πu, g3Σg+, i3Πg, j3Δg, f3Σu+, k3Πu, r3Πg, and s3Δg, are calculated by Gryzinski method in the present study. The cross sections for these states show a significant dependence on the threshold energy. The isotope effect of the cross sections for H2 and D2 is discussed. The computed cross sections of the electronic states with n= 1–4 from threshold up to 10 keV are fitted. The corresponding Maxwellian rate coefficients are derived from those cross sections with electron temperature from 1 to 10 eV.

Estimation of Electron Impact Ionization Rates of Li Using a Non-Maxwellian Distribution Function

We report an estimate of the cross-section and rate of electron-impact ionization of Li. The FAC code (Flexible Atomic Code) is used in order to determine the cross-section and to calculate the level of energy. We evaluate the effect of electron energy distribution functions on the measurement of the ionization rate for a non-Maxwellian energy distribution, if the fraction of hot electrons is small. In several types of plasma, it has been observed that certain (hot) electrons are governed by a non-Maxwellian energy distribution. These electrons affect the line spectra and other characteristics of plasma. By using a non-Maxwellian distribution of energies, we revealed the sensitivity of the electron-impact ionization rate of Li to types of the electron energy distribution and to the fraction of hot electrons.