Electron-impact Single Ionization Research Articles

Universal statistical approach to radiative and collisional processes with multielectron ions in plasmas

The universal statistical approach for calculation of radiative and collisional processes with multielectron ions in plasmas is developed. It is based on the atomic structure representation similar to that used in a condensed medium. The distribution of local atomic electron density determines the set of elementary excitations with classical plasma frequency. The statistical method is tested by the calculations of the total electron impact single ionization cross-sections, ionization rates and radiative losses of various ions. In the coronal limit the radiative losses of heavy plasma impurities with any type of multielectron ions are determined by the excitation of collective atomic oscillations due to collisions with plasma electrons. It is shown that for low plasma densities the tungsten ions total radiative loss scatter within universal statistical approach does not exceed similar results of current complex numerical codes in the wide range of plasma temperatures. The general expression for the radiative losses in the case of the intermediate state between limiting cases of coronal and Boltzmann population distributions is derived as well. The total electron impact ionization cross-sections and ionization rates for ions of various charge stages for a wide range of elements from Ar to U are compared with experimental and conventional complex code data showing satisfactory agreement. As the universal statistical method operates in terms of collective excitations, it implicitly includes direct and indirect ionization processes.

Kinematically complete study of low-energy electron-impact ionization of neon: Internormalized cross sections in three-dimensional kinematics

As a further test of advanced theoretical methods to describe electron-impact single-ionization processes in complex atomic targets, we extended our recent work on $\mathrm{Ne}(2p$) ionization [X. Ren, S. Amami, O. Zatsarinny, T. Pfl\uger, M. Weyland, W. Y. Baek, H. Rabus, K. Bartschat, D. Madison, and A. Dorn, Phys. Rev. A 91, 032707 (2015)] to $\mathrm{Ar}(3p$) ionization at the relatively low incident energy of ${E}_{0}=66$ eV. The experimental data were obtained with a reaction microscope, which can cover nearly the entire $4\ensuremath{\pi}$ solid angle for the secondary electron emission. We present experimental data for detection angles of 10, 15, and ${20}^{\ensuremath{\circ}}$ for the faster of the two outgoing electrons as a function of the detection angle of the secondary electron with energies of 3, 5, and 10 eV, respectively. Comparison with theoretical predictions from a $B$-spline $R$-matrix (BSR) with pseudostates approach and a three-body distorted-wave (3DW) approach, for detection of the secondary electron in three orthogonal planes as well as the entire solid angle, shows overall satisfactory agreement between experiment and the BSR results, whereas the 3DW approach faces difficulties in predicting some of the details of the angular distributions. These findings are different from our earlier work on $\mathrm{Ne}(2p$), where both the BSR and 3DW approaches yielded comparable levels of agreement with the experimental data.

Electron impact single and double ionization cross sections of Hg atoms

Theoretical studies of electron impact single and double ionization cross sections of Hg atoms have been performed in the binary encounter approximation. Direct double ionization has been investigated in the modified double binary encounter model. Accurate expression of σ ΔE cross section for energy transfer ΔE and the Hartree–Fock velocity distributions for the target electrons have been used throughout the calculations. The present results of single ionization cross sections are in good agreement with the experimental observations. In the case of double ionization, the theoretical cross sections for direct double ionization show overall satisfactory agreement with the experiment. The calculated single and direct double ionization cross sections substantiate the viewpoint that only the direct processes lead to double ionization of Hg and there is no role of Auger effect concerning the measured data of double ionization.

Statistical model of electron impact ionization of multielectron ions

The statistical method for ab initio calculations of the electron impact ionization cross sections of multielectron ions and related ionization rates is developed. It is created based on an idea of collective excitations of atomic electrons alike in condensed medium. The Thomas–Fermi model density distribution of atomic electrons is assumed and their collective oscillations are described by the local plasma frequency model. Using a proposed statistical approach the calculations of the total single electron impact ionization cross sections of multielectron ions for several chosen chemical elements from argon up to uranium, taken in the various charge states, are performed and compared with available experimental and theoretical data, demonstrating a satisfactory agreement.

Plasma rate coefficients for electron-impact ionization of Xeq+ ions (q = 8, …, 17)

Plasma rate coefficients (PRCs) for electron-impact single ionization of ground-state Xeq+ ions () in the temperature range 2 × 105 − 2 × 107 K have been derived from a combination of experimental cross-section data and results of distorted-wave calculations. For Xe8+ and Xe9+ new measurements were performed and thoroughly analyzed with respect to the contributions from different ionization mechanisms and the effects of long-lived excited states in the parent ion beams that had been employed in the experiments. In the same manner, previously published experimental data for the higher charge states were analyzed to extract the ground-configuration ionization cross sections and to derive the associated PRCs. The resulting temperature-dependent PRC functions were parameterized and the associated parameters are provided in tabular form. With the exception of Xe8+ the absolute uncertainties of the inferred rate coefficients are estimated to be For Xe8+ the uncertainties are due to the necessary correction for strong metastable-ion contributions to the measured cross sections.

Electron Impact Single Ionization of Kr and Xe

Theoretical studies of electron impact single ionization cross sections of Kr and Xe atoms have been performed in the Binary Encounter Approximation (BEA). Accurate expression of σΔE (cross-section for energy transferΔE) and the Hartree-Fock (HF) velocity distributions for the target electrons have been used throughout the calculations. The present results of single ionization cross sections are in good agreement with the experimental observations.

Electron-impact ionization of Se2+

Absolute cross sections for electron-impact single and multiple ionization of Se2+ ions were measured using the dynamic-crossed-beams technique over the energy range from the ionization threshold to 500 eV and compared to direct ionization cross sections predicted by the Lotz semi-empirical formula. The single-ionization cross section appears to be dominated by excitation-autoionization of the 4s and 3d inner subshells. The double-ionization measurements are reasonably well accounted for by the semi-empirical fitting formula of Shevelko et al that includes both direct double ionization of the outer 4p subshell and single ionization of the 3p and 3d subshells followed by autoionization. In addition to direct triple ionization, 3p and 3s ionization followed by double autoionization and excitation of the 3p and 3s subshells followed by triple autoionization likely contribute to the triple ionization cross section.

Electron-impact ionization of Se3+

Absolute electron-impact single and multiple ionization cross-section measurements for Se3+ ions were performed using the dynamic-crossed-beams technique over the energy range from the ionization threshold to 1 keV. The experimental single ionization cross section for Se3+ shows evidence of significant contributions of 4s–nl (n ≥ 6) and 3d–nl (n ≥ 4) inner-shell excitation-autoionization. The cross sections for double and triple ionization are dominated by ionization-autoionization and ionization-double autoionization of a 3p or 3s electron, respectively. The measurements were compared with the direct ionization cross sections predicted by the Lotz semi-empirical formula for direct ionization. The maximum values of cross sections for single, double, and triple ionization are compared.

Electron impact multiple ionization of C+ and N+ and O+ ions

Absolute cross sections for electron impact single and multiple ionization of C+, N+ and O+ ions leading to the formation of Cq+ (q=2-4), Nq+ (q=2-5) and Oq+ (q=2-5) are reported in the energy range extending from the respective thresholds up to 2.5 keV. The general feature of the measured cross sections is investigated.

Electron-impact ionization of 4d-shell xenon and tin ions

Electron-impact single ionization of xenon and tin ions for charge states where the 4d-subshell is the outermost has been investigated. Measured cross sections have been analyzed in detail by comparing with configuration-averaged distorted wave (CAWD) calculations. Contributions of different direct- and indirect ionization processes have thus been quantitatively revealed.

Accelerating spectral atomic and molecular collisions methods with graphics processing units

We present a computation method to accelerate the calculation of the Hamiltonian of a three-body time independent Schrödinger equation for collisions. The Hamiltonian is constructed with one dimensional (basis overlaps) and two dimensional (interparticle interaction) integrals that are mapped into a computational grid in a Graphics Processing Unit (GPU). We illustrate the method for the case of an electron impact single ionization of a two electron atom. This proposal makes use of a Generalized Sturmian Basis set for each electron, which are obtained numerically on a quadrature grid that is used to compute the integrals in the GPU. The optimal computation is more than twenty times faster in the GPU than the calculation in CPU. The method can be easily scaled to computers with several Graphics Processing Units or clusters.

Measurement of Double Differential Cross-Section for Electron Impact Ionization of Argon at 348 eV

Renewed interest in measuring cross-sections for scattering electrons or positrons by noble gas atoms at intermediate energies has recently led to test various theoretical approximations. Ionization of the noble gases such as He, Ne, Ar, Kr, and Xe by electron impact is an important process in collision physics. Argon has been studied from the discharge point of view for more than 100 years and interest in this gas is due to several important fundamental and technical considerations. Cross-sections for electron-impact ionization have been measured and calculated since the early days of collision physics because of their importance to the kinetics and dynamics of collisions in relevance to many practical applications. Previous experimental measurements of double di erential cross-sections (DDCS) by electron impact for targets rather than helium are very few. The most itemized study is that of Opal et al. [1]. They presented DDCS data for several gases at di erent incident energies of a wide angular range. The literature contains the results from several experimental measurements on the double di erential cross-section studies of Ar. The elastic scattering of electrons by noble gases has been extensively studied and a large number of either theoretically or experimentally obtained relative and absolute di erential cross-sections are available at various incident electron energies and scattering angles. The critical minima appearing in Ar DCS spectra are the most sensitive test for comparison of experimental and theoretical results and, hence, give good possibilities for testing di erent theoretical models. DuBois and Rudd [2] measured DDCS for 100 500 eV electron impact of Ar including Ne, N2, and H2 data. Hippler et al. [3] and Chaudhry et al. [4] reported energy distributions of ejected electrons in double or (multiple) ionization of rare gases 300 eV to 10 keV electron impact. Another work is done by Santos et al. [5] at 500 750 and 1000 eV electron impact single or multiple ionization DDCSs of Ar. Yates and Khakoo [6] have presented DDCSs of Ar for near threshold electron impact single ionization of Ar at 17, 18, 20, and 30 eV. In this work, we used Ar target as a typical that is reasonable to expect to understand ionization mechanism of atomic systems. We have measured DDCS for asymmetric geometry for di erent kinematical conditions.

Electron impact ionization of silicon and germanium atom

Theoretical studies of electron impact single ionization cross sections of Si and Ge atoms have been performed in the binary encounter approximation (BEA) including exchange and interference as given by Vriens and the Hartree-Fock (HF) velocity distributions for the target electrons have been used throughout the calculations. The present results of single ionization cross sections are in good agreement with the experimental observations.

A four-body approach to electron-impact single ionization of helium atoms

A four-body approach based on the three-Coulomb distorted wave (3CDW) model is applied to study of the electron-impact single ionization of helium atoms. Triply differential cross sections (TDCS) are calculated for different values of the incident and ejection energies and various amounts of the scattering angles. The ejection angular distribution of the TDCS in general exhibits two peaks, binary and recoil peaks. The obtained results are compared with the available experimental data as well as other theoretical predictions. The comparison shows a good agreement between the present calculations and the measurements. Also, the obtained results are compatible with the other theories.

Angular distributions for the electron-impact single ionization of sodium and magnesium

We present angular distributions for the electron-impact single ionization of sodium and magnesium at intermediate incident electron energies. The results are obtained from a full-dimensionality solution of the two-active-electron time-dependent Schr\odinger equation using the time-dependent close-coupling method. We compare calculated angular distributions with existing measurements. We find good overall agreement with measurements over a range of incident electron energies in both cases. We also calculate angular distributions for ejection configurations in which no measurements are currently available.

Electron-impact ionization of moderately charged xenon ions

Absolute and energy scanned cross sections for the electron-impact single ionization of Xeq + (q = 10–17) atomic ions are measured by employing a crossed-beams technique in the collision energy range from threshold to 1000 eV. Direct ionization and indirect excitation-autoionization cross sections are calculated using a configuration-average distorted-wave method for the ground and first same parity excited configuration of the Xeq + (q = 10–17) atomic ions. Both the crossed-beams experiment and distorted-wave theory show a steady decrease in the ionization cross section as the charge of the ion increases. The disagreements between experiment and theory are partly attributed to the many metastable levels of ground and excited configurations found in the ion beam.

Multiple ionization of C+, N+ and O+ ions by fast electron impact

Absolute cross sections for electron impact single and multiple ionization of C+, N+ and O+ ions leading to the formation of Cq + (q = 2–4), Nq + (q = 2–5) and Oq + (q = 2–5) are reported. The animated crossed beam method is applied in the energy range extending from the respective thresholds up to 2.5 keV. The concerned target ions belong to the second row of the periodic table, with configurations 2s22px (x = 1–3). The maximum cross sections for the multiply charged products Cq + are found to be in the range from 2.3× 10−20 cm2 (for C4 +) up to 6.3× 10−17 cm2 (for C2 +); for Nq + they range from 3.0× 10−22 cm2 (for N5 +) up to 5.1× 10−17 cm2 (for N2 +) and, lastly, for Oq + they range from 5.5× 10−22 cm2 (for O5 +) up to 5.2× 10−17 cm2 (for O2 +). The corresponding threshold energies are found to be in satisfactory agreement with spectroscopic values. The general feature of the measured cross sections is investigated. Their values for single ionization are reasonably explained by the calculations using the Coulomb–Born approximation with exchange, while those for multiple ionization are found to agree well with the semiempirical model for q = 3, but they appear to be notably overestimated by a semiempirical Bethe–Born-type formula when q > 3.

Detailed investigation of electron-impact single-ionization cross sections and plasma rate coefficients of N-shell tin ions

Electron-impact single-ionization cross sections of Snq + ions in charge states q = 4–13 with 4d[10 − (q − 4)] outer-shell configurations have been studied in the energy range from the corresponding thresholds up to 1000 eV. Absolute cross sections and fine-step energy-scan data have been measured employing the crossed-beams technique. Contributions of different ionization mechanisms have been analysed by comparing the experimental data with calculations employing the configuration-averaged distorted wave approximation. Ionization plasma rate coefficients inferred from the experimental data are also presented.

Influence of screening effect on double differential cross section and single differential cross section for (e, 2e) process of helium

The double differential cross sections for electron impact single ionization of helium at incident energies of 32.5, 36.5 and 40.7 eV are calculated by using the DS3C model. The calculated results are compared with the experimental date. The exchange effects are discussed. The single differential cross section for electron impact single ionization of helium is obtained by integrating the double differential cross sections over the angle of the ejected electron. The single differential cross sections of helium at incident energies of 32.5, 36.5, 40.7 and 50 eV are calculated by using the 3C model and the DS3C model. The calculated results are compared with the experimental date. The structure of the cross section is analysed and the contribution of exchange effect to the corss section is discussed.

Applications of Artificial Neural Networks to Proton and Electron Impact Ionization of Biologically Relevant Atoms and Molecules

We use Artificial Neural Networks (ANNs) to study proton and electron impact single ionization of biologically relevant atoms and molecules. In these processes, an incident proton or electron collides with a target atom or molecule causing a single electron to be ionized from the target. The process of ionization is biologically relevant for two reasons. Firstly, ionization results in reactive ions that are able to take part in damaging chemical reactions. Secondly, free electrons have been shown to result in DNA strand breaks, which can lead to cell death. While atomic and molecular collisions have been studied experimentally for decades, most of the available data is for noble gas atoms and small diatomic molecules. ANNs are computer programs that are trained to learn patterns in data and make predictions for cases where no data exists. They have been widely used in other fields, but this is one of the first applications of ANNs to atomic and molecular collision processes. In this work, we use the available experimental data to train the ANN, and then make predictions for biologically important target atoms and molecules where no data currently exists.