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We determined the size distribution of helium droplets produced in a pulsed beam in the condensation regime from the gas phase. Following electron-impact ionization, the mass-to-charge ratios of the positively charged droplets were determined by measuring their kinetic energies and velocities using an electrostatic cylindrical deflector setup. Over a range of different source conditions, we observed bimodal velocity distributions and log-normal size distributions. Our results are similar to those reported for continuous beams, but with mean sizes larger by a factor of around 100. The log-normal size distributions reported here differ strongly from the exponential distributions recently reported for a pulsed beam produced using a different nozzle design. [ABSTRACT FROM AUTHOR]

We propose a semi-empirical formula for the cross section of ionization by electron impact. The formula involves adjustable parameters which are determined by comparison with measured or numerically calculated cross sections. In the latter case, the ions are perturbed by their environment which is a high-density plasma. As a consequence, the cross section is significantly modified. We investigate Be-like carbon, nitrogen and oxygen as well as aluminum ions. We also show that the formula is well-suited for interpolation and extrapolation. Knowing the cross section, we calculate the rate coefficient within the Boltzmann and Fermi–Dirac statistics. In the first case, the rate can be calculated analytically. In the second one, it can be expressed in terms of special functions, but the numerical evaluation is more convenient while providing accurate results. Our results are compared to experiment and to other calculations. [ABSTRACT FROM AUTHOR]

Electron-impact ionization (EII) processes are essential for modelling high-temperature plasma in quite different research areas, from astrophysics to material science to plasma and fusion research and in several places elsewhere. In most, if not all, of these fields, partial and total EII cross sections are required, and often for a good range of electron energies, in order to determine, for instance, the level population of ions and spectral line intensities in plasma under both local and non-local thermodynamic equilibrium conditions. To obey these needs, various kinds of semi-empirical EII cross sections have been applied in practice, often simply because of the large computational demands in dealing explicitly with two free electrons within the continuum. Here, we expand Jac, the Jena Atomic Calculator, to provide such empirical EII cross sections for (most) atoms and ions across the periodic table. Five empirical models from the recent literature have been implemented to support a simple and rapid access to the partial EII cross sections for electrons from a (partly filled) shell (nℓ)q as well as the total ionization cross sections. We here restrict ourselves to the direct part of the EII cross section, whereas the impact excitation of electrons with subsequent autoionization and the resonant electron capture with double autoionization have been left aside in this first implementation. Rapid access to the (direct) EII cross sections will help already to better understand the role of electron-impact processes in the diagnostics of fusion plasma or the interpretation of astrophysical spectra.

Argon is being considered as an injected impurity to mitigate damage to divertors of DEMO caused by excessive heat flux. For a comprehensive understanding of Ar plasma, carefully evaluated atomic data are required. In this study, the electron-impact ionization cross-sections and rate coefficients for all atomic ions in the argon isonuclear sequence are calculated using the level-to-level distorted wave approximation. The calculated cross-sections and rate coefficients are compared with experimental data and other theoretical calculations. The calculated values are consistent with results reported in the literature, with differences not exceeding 20%. We fit the calculated cross-sections using an empirical formula. Additionally, we combine our ionization rate coefficients with the dielectronic- and radiative-recombination rate coefficients from other studies to determine the ionization balance. The obtained data are expected to be useful for plasma modelling involving argon impurities. [ABSTRACT FROM AUTHOR]

In this manuscript, we present our calculations of detailed electron-impact single ionization cross-sections for tungsten ions, spanning charge states W 38 + − W 45 + . The level-to-level distorted-wave method implemented in the flexible atomic code (FAC) was used for calculation. Comparison between the present level-to-level distorted wave treatment and previous configuration-averaged calculations has been performed for the W 45 + ion, and we explore the possible reason for the difference observed between two calculations. We demonstrate the importance of radiative damping on the total electron-impact ionization cross-section for the W 43 + ion. Present calculations provide missing cross-sections for W 38 + − W 45 + . The data obtained are expected to be useful for modeling plasmas for fusion applications, especially for the ITER community. [ABSTRACT FROM AUTHOR]

In the present work, we assess the effectiveness of singly differential cross sections (SDCS) due to electron-impact ionization by invoking the binary-encounter-Bethe (BEB) model on various atomic and molecular targets. The computed results were compared with the experimental and theoretical data. A good agreement was observed between the present and the available results. This agreement improves as the incident energy of the projectile increases. The model can be applied to compute the SDCS for the ions produced due to the electron-impact dissociative ionization process and the average energy due to the secondary electrons. Both these quantities are of interest in plasma processing and radiation physics. [ABSTRACT FROM AUTHOR]

The article is devoted to a brief description of the ATOM computer program system, designed to study the structure, transition probabilities and cross sections of various processes in multielectron atoms. The theoretical study was based on the concept of a computational experiment, the main provisions of which are discussed in the article. The main approximate methods used in the system of programs for taking many-electron correlations into account and determining their role in photoionization processes, elastic and inelastic electron scattering, the decay of vacancies, and many others are presented. The most significant results obtained with this software are listed. [ABSTRACT FROM AUTHOR]

The Binary-Encounter Bethe approach was applied to the estimation of total ionization induced by electron impact in metastable states of diatomic molecules. The cross sections recently obtained for N 2 and CO are reviewed and the new results for H 2 are presented, discussing their reliability through the comparison with other theoretical methods. [ABSTRACT FROM AUTHOR]

The electron-impact ionization of lithium-like ions C3+, N4+, O5+, Ne7+, and Fe23+ is studied using a combination of two-potential distorted-wave and R-matrix methods with a relativistic correction. Total cross sections are computed for incident energies from 1 to 10 times of ionization energy and better agreements with the experimental results are obtained in comparison with the theoretical data available. It is found that the indirect ionization processes become significant for the incident energy larger than about four times of the ionization energy. Contributions from the exchange effects along the isoelectronic sequence are also discussed and found to be important. The present method can be used to obtain systematic ionization cross sections for highly charged ions across a wide incident energy range. [ABSTRACT FROM AUTHOR]

In this manuscript, we present our calculations of detailed electron-impact single ionization cross-sections for tungsten ions, spanning charge states W38+− W45+. The level-to-level distorted-wave method implemented in the flexible atomic code (FAC) was used for calculation. Comparison between the present level-to-level distorted wave treatment and previous configuration-averaged calculations has been performed for the W45+ ion, and we explore the possible reason for the difference observed between two calculations. We demonstrate the importance of radiative damping on the total electron-impact ionization cross-section for the W43+ ion. Present calculations provide missing cross-sections for W38+− W45+. The data obtained are expected to be useful for modeling plasmas for fusion applications, especially for the ITER community.

Electron-impact ionization cross sections are investigated for the ground levels of N 2 + and N 3 + ions. Additionally, the long-lived energy levels of the N 2 + 2 s 2 p 2 and N 3 + 2 s 2 p configurations are analyzed. Study includes both direct and indirect ionization processes. Contribution of the excitation–autoionization (EA) channels to the ionization cross sections is approximately 15% to 23% for both ions. Convergence of the EA cross sections is analyzed by considering excitations up to shells with the principal quantum numbers n ⩽ 20. The obtained results are compared to available experimental data for the N 2 + and N 3 + ions. • Indirect process contributes 15% - 23% for configurations of the N 2 + ion and long-lived levels of the N 3 + ion. • Excitations to shells with 11 ⩽ n ⩽ 20 produce up to ∼ 15% of the EA cross sections for the N 2 + ion. • Good agreement with measurements and the previous CADW and RMPS calculations is obtained for the N 3 + ion. [ABSTRACT FROM AUTHOR]

In the present work, we assess the effectiveness of singly differential cross sections (SDCS) due to electron-impact ionization by invoking the binary-encounter-Bethe (BEB) model on various atomic and molecular targets. The computed results were compared with the experimental and theoretical data. A good agreement was observed between the present and the available results. This agreement improves as the incident energy of the projectile increases. The model can be applied to compute the SDCS for the ions produced due to the electron-impact dissociative ionization process and the average energy due to the secondary electrons. Both these quantities are of interest in plasma processing and radiation physics.

The article is devoted to a brief description of the ATOM computer program system, designed to study the structure, transition probabilities and cross sections of various processes in multielectron atoms. The theoretical study was based on the concept of a computational experiment, the main provisions of which are discussed in the article. The main approximate methods used in the system of programs for taking many-electron correlations into account and determining their role in photoionization processes, elastic and inelastic electron scattering, the decay of vacancies, and many others are presented. The most significant results obtained with this software are listed.

The Binary-Encounter Bethe approach was applied to the estimation of total ionization induced by electron impact in metastable states of diatomic molecules. The cross sections recently obtained for N2 and CO are reviewed and the new results for H2 are presented, discussing their reliability through the comparison with other theoretical methods.

Near-threshold photoionization cross sections for several aluminum clusters have been estimated from the ionization efficiency curves. Their magnitude raises the possibility that the edge of a collective electron resonance (surface plasmon) may contribute to the photoemission channel. On the other hand, electron impact ionization efficiently produces multiply charged metal cluster ions and is unaccompanied by noticeable fragmentation. Consequently it does not appear to involve collective excitations. [Display omitted] • Cross sections of aluminum nanoclusters have been determined. • Interaction between surface plasmon resonances and photoionization is suggested. • Electron impact ionization produces multiply charged clusters. • Electron impact ionization appears to proceed via a direct process. [ABSTRACT FROM AUTHOR]

We investigate ionization of atomic hydrogen by electron- and positron-impact. We apply the Coulomb–Born (CB1) approximation, various modified CB1 approximations, the three body distorted wave (3DW) approximation, and the time-dependent close-coupling (TDCC) method to electron-impact ionization of hydrogen. For electron-impact ionization of hydrogen for an incident energy of approximately 76.45 eV, we obtain a deep minimum in the CB1 triply differential cross section (TDCS). However, the TDCC for 74.45 eV and the 3DW for 74.46 eV gave a dip in the TDCS. For positron-hydrogen ionization (breakup) we apply the CB1 approximation and a modified CB1 approximation. We obtain a deep minimum in the TDCS and a zero in the CB1 transition matrix element for an incident energy of 100 eV with a gun angle of 56.13 ° . Corresponding to a zero in the CB1 transition matrix element, there is a vortex in the velocity field associated with this element. For both electron- and positron-impact ionization of hydrogen the velocity field rotates in the same direction, which is anticlockwise. All calculations are performed for a doubly symmetric geometry; the electron-impact ionization is in-plane and the positron-impact ionization is out-of-plane.

Collisional processes and details of atomic structure of heavy many-electron atoms and ions are not yet understood in a fully satisfying manner. Experimental studies are required for guiding new theoretical approaches. In response to fusion-related needs for collisional and spectroscopic data on tungsten atoms in all charge states, a project has been initiated in which electron-impact and photon-induced ionization as well as photorecombination of Wq+ ions are studied. Cross sections and rate coefficients were determined for charge states q ranging from q = 1 to q = 5 for photoionization, for q = 1 up to q = 19 for electron-impact ionization and for q = 18 to q = 21 for electron-ion recombination. An overview, together with a critical assessment of the methods and results is provided.

The partial and total ionization cross sections for N 2 in gas phase by electron impact in a wide energy range have been measured by ion imaging mass spectrometer. The results are put on an absolute scale by normalizing the data of N 2 + to that of Ar + from N 2 –Ar mixture target. The overall errors are evaluated by considering various kinds of uncertainties. Comparisons are made with the previous measurements. [ABSTRACT FROM AUTHOR]

The sensitivity of an electron–ion crossed-beams experiment is mainly determined by the densities of both beams in the interaction region. Aiming at the extension of the available range of accessible electron energies and densities, a new high-power electron gun has been developed and fabricated. It delivers a ribbon-shaped beam with currents of up to 1 A at variable energies reaching 3500 eV at the maximum. The design goals of the gun are being met by using a configuration of electrodes, which allows for a variety of operation modes. Here, we report on the results of the ongoing tests of the new electron gun. In particular, electron-impact ionization cross sections of He + and Xe 5+ ions were measured employing the animated crossed-beams technique. The results are in excellent agreement with literature data. [ABSTRACT FROM AUTHOR]

In this work, we derive X-ray production cross-sections from electron-impact ionization cross-sections for Ne, Ar, Kr, Xe, Rn, and Uuo, calculated in the modified relativistic binary-encounter-Bethe model, and using as the only input parameter the binding energies obtained in the Dirac-Fock approach. Radiative and radiationless transition probabilities necessary to compute the inter- and intra-shell atomic yields were calculated in the same approach. Shell electron-impact ionization cross-sections and X-ray production cross-sections are compared with the corresponding cross-sections retrieved from the National Institute of Standards and Technology Reference Database and available experimental data. [ABSTRACT FROM AUTHOR]

We report the measurement of Ag K-shell ionization cross-section by electron impact in the range 50–100 keV and review the experimental data found in the literature. The sample consisted in a thin film of Ag evaporated on a thin C backing. The x-ray spectra generated by electron bombardment in the São Paulo Microtron were observed with a planar HPGe detector. The ratios between characteristic and bremsstrahlung x-ray yields were transformed to ionization cross sections with the help of theoretical atomic-field bremsstrahlung cross sections. The measured cross sections are compared with existing experimental values and calculations based on the semi-relativistic distorted-wave Born approximation. According to our experiment, the ratio of Ag K β to K α x-ray intensities is 0.2018(24). [ABSTRACT FROM AUTHOR]

In the past two decades, the electron–ion merged-beams technique has extensively been exploited at heavy-ion storage rings equipped with electron coolers for spectroscopic studies of highly charged ions as well as for measuring absolute cross sections and rate coefficients for electron–ion recombination and electron-impact ionization of multiply charged atoms ions. Some recent results are highlighted and future perspectives are pointed out, in particular, in view of novel experimental possibilities at the FAIR facility in Darmstadt and at the Cryogenic Storage Ring at the Max-Planck-Institute for Nuclear Physics in Heidelberg. [ABSTRACT FROM AUTHOR]

Absolute M α x-ray production cross sections have been measured and calculated for heavy elements Au, Pb, Bi, and U for electron incident energies from the ionization threshold up to 38 keV. The experimental cross sections were deduced from M x-ray intensities emitted from ultrathin samples of the elements of interest deposited onto self-supporting C films. The measurements were performed using two electron microprobes and several wavelength-dispersive spectrometers. X-ray intensities were converted into x-ray production cross sections by using estimated values of the number of incident electrons, target thickness, and spectrometer efficiency. Experimental results are compared with calculated cross sections using different predictive formulae. Good agreement is found between the measured cross sections and the predictions from the distorted-wave Born approximation, which indicates that this approximation is suited for the calculation of M-shell ionization cross sections of heavy elements. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

• Tungsten is an important metal as it is under consideration as a plasma-facing material in the thermonuclear experiment such as ITER. • Electron-impact ionization data is required to model tungsten impurities that may sputter into the fusion plasma. • This work present the new and the only theoretical electron-impact ionization data for W7+. • We demonstrated the importance of the metastable states, their contribution also should be considered for adjacent ions of tungsten. 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. [ABSTRACT FROM AUTHOR]

A method for determining photoionization cross sections based on comparison of the characteristics of electron- and photon-impact processes is described, discussed, and demonstrated to have many advantageous features. [ABSTRACT FROM AUTHOR]

A prototype x-ray system based on a liquid-metal-jet anode was evaluated within the framework of the LABSYNC project. The generated spectrum was measured using a CZT-based spectrometer and was compared with spectra simulated by three Monte Carlo codes: MCNPX, PENELOPE and EGS5. Notable differences in the simulated spectra were found. These are mainly attributable to differences in the models adopted for the electron-impact ionization cross section. The simulation that more closely reproduces the experimentally measured spectrum was provided by PENELOPE. [ABSTRACT FROM AUTHOR]

An analysis is presented of measured and calculated cross sections for inner-shell ionization by electron impact. We describe the essentials of classical and semiclassical models and of quantum approximations for computing ionization cross sections. The emphasis is on the recent formulation of the distorted-wave Born approximation by Bote and Salvat [Phys. Rev. A 77, 042701 (2008)] that has been used to generate an extensive database of cross sections for the ionization of the K shell and the L and M subshells of all elements from hydrogen to einsteinium (Z = 1 to Z = 99) by electrons and positrons with kinetic energies up to 1 GeV.We describe a systematic method for evaluating cross sections for emission of x rays and Auger electrons based on atomic transition probabilities from the Evaluated Atomic Data Library of Perkins et al. [Lawrence Livermore National Laboratory, UCRL-ID-50400, 1991]. We made an extensive comparison of measured K-shell, L-subshell, and M-subshell ionization cross sections and of Lα x-ray production cross sections with the corresponding calculated cross sections. We identified elements for which there were at least three (for K shells) or two (for L and M subshells) mutually consistent sets of cross-section measurements and for which the cross sections varied with energy as expected by theory. The overall average root-mean-square deviation between the measured and calculated cross sections was 10.9% and the overall average deviation was -2.5%. This degree of agreement between measured and calculated ionization and x-ray production cross sections was considered to be very satisfactory given the difficulties of these measurements. [ABSTRACT FROM AUTHOR]

Highlights: [•] We have calculated electron-impact ionization cross sections for the ground and metastable levels of W+ forming W2+ using flexible atomic code based on a distorted wave approximation. [•] Sensitivity of direct ionization cross section to a single atomic local central potential has been investigated. [•] All possible excitation–autoionizations of dipole-allowed E1 and non-E1, 5d, 6s→nl (5≤ n ≤30) and 4f, 5s, 5p → nl (n =5,6) are considered with the detailed branching ratios. [Copyright &y& Elsevier]

Abstract: The study of structure and collision processes of three- and four-body problems has seen an extraordinary progress in the last decades. This progress has been in part associated to the incredible fast growth of the computer capabilities. However, the tools used to solve structure problems are different from those corresponding to the treatment of collision processes. In this review, we provide the theoretical framework and a selection of results for both structure as well as collision problems using only one technique that we have developed in the last few years, based on the use of Generalized Sturmian functions. We present results obtained in structure studies of isolated and confined two-electron atoms, and exotic and molecular systems. The same technique is applied to the study of various benchmark problems for the single ionization of hydrogen and the double ionization of helium by electron impact. In this way, we demonstrate that the Generalized Sturmian method can be successfully applied to the treatment of both types of problems. [Copyright &y& Elsevier]

Abstract: The immense progress in the field of electron–atom scattering, where pure Coulomb potentials are involved, has been translated to collision processes in Debye plasmas. The Debye–Hückel potential is used to describe plasma Coulomb screening effects depending on the temperature and density of the plasma. We provide benchmark results of electron–helium scattering for momentum transfer cross sections, discrete excitation and ionization over a broad range of incident energies and Debye radii. [Copyright &y& Elsevier]

Abstract: Dynamically screened three-Coulomb-wave (DS3C) model is applied to study single ionization of helium by 102 eV electron impact. Fully differential cross sections (FDCS) are calculated at different scattering angle of (8°, 10°, 15°, 20°) in the perpendicular plane asymmetric geometry. The results are compared with experimental data and theoretical predictions from a three-Coulomb wave function (3C) approach, convergent close-coupling calculation (CCC), as well as second-order distorted-wave Born method (DWB2). It is shown that three-body coupling effects are important for the perpendicular plane geometry. [Copyright &y& Elsevier]

Abstract: We describe improvements to the fast-beam apparatus that has been used extensively for electron-impact ionization cross section measurements for atoms, molecules, and free radicals in our group for the past 15 years. A high-intensity, dispenser-type electron emitter capable of producing an electron beam of more than 2mA at electron energies above 50eV is used instead of a conventional indirectly heated, oxide-coated electron source. We also replaced the channel electron multiplier by a position-sensitive, triple multi-channel plate ion detector. Experiments using well-established ionization cross sections in conjunction with extensive ion trajectory simulations were carried out to verify the performance of the modified fast-neutral-beam apparatus. This apparatus was subsequently employed in the measurement of absolute partial cross sections for the formation of various singly charged positive ions produced by electron impact on SiCl3 for impact energies from threshold to 200eV. A comparison with calculations and with the previously reported ionization cross section for SiCl4, SiCl2, and SiCl is also made. [Copyright &y& Elsevier]

Abstract: We report results of the calculation of electron-impact ionization cross section for the lanthanide atoms Ce through Lu, which are collectively referred to as the (4f) transition-metals, using the Deutsch-Märk (DM) formalism. The lanthanides are characterized by an unfilled (5d) sub-shell and a partially filled (4f) sub-shell. The strong correlation of the open (4f) sub-shell with the (5d) sub-shell and the considerable uncertainty in the binding energies of the electrons in the (4f), (5s), (5p), (5d), and (6s) sub-shells as well as in their energetic ordering are shown to affect the choice of parameters that are required for the cross section calculations in the DM model as inferred from a comparison between the calculated DM cross sections and available experimental cross section data. [Copyright &y& Elsevier]

Abstract: We report results of the calculation of electron-impact ionization cross-sections for atoms with atomic numbers Z in the intermediate range of Z-values (20< Z <56) using the DM formalism. For atoms with Z-values in this range (which contains many atoms of practical importance), there are some experimentally determined ionization cross-sections, but there has only been a single systematic theoretical study from 30 years ago, which was based on the Born approximation. The Born approximation tends to yield cross-sections which show an “overestimation” in the energy regime of the cross-section maximum compared to experimental data. The DM approach, on the other hand, has adequately reproduced the region of the cross-section maximum for many low-Z atoms as well as for the heavier rare gases. In the present case of atoms with Z-values from 20 to 56, the DM calculation typically shows a cross-section maximum lower than that predicted from the Born approximation by 25–50%, except for Xe, Ni, Cd, and Pd. The Born approximation and the DM formalism yield cross-sections that converge at higher impact energies. [Copyright &y& Elsevier]

Abstract: A simple-to-use empirical model for the calculation of electron impact single K-shell ionization total cross sections for 60 atomic targets from H to U (1≤ Z ≤92) and the energies from threshold to ultra-relativistic range is described. Simplified BELL formula [K.L Bell, H.B. Gilbody, J.G. Hughes, A.E. Kingston, F.J. Smith, J. Phys. Chem. Ref. Data 12 (1983) 891] is used in the proposed model by incorporating in it both the ionic and relativistic corrections. The predicted K-shell ionization cross sections are compared with recently measured experimental data. Better agreement is found for all atoms considered except Xe. Moreover, the calculated results are also compared with other theoretical methods and empirical formulae. The predicted results achieve a level of agreement with both experimental data those are better than the predictions from the existing theoretical methods and empirical models. With the inherent simplicity of its structure, this model may be a prudent selection for the users where fast generation of electron impact single K-shell ionization total cross sections are required. [Copyright &y& Elsevier]

Abstract: DC magnetron sputtering was carried out using a microwave plasma to enhance the ionization of sputtered aluminum atoms at a low gas pressure. The ionization fraction of sputtered aluminum atoms measured using a gridded thickness monitor was 40% at a low gas pressure of 0.05Pa. The collision frequency for the ionization of sputtered aluminum atoms calculated theoretically under the assumption of electron-impact ionization was in good agreement with the experimental results. [Copyright &y& Elsevier]

Abstract: The electron impact single ionization cross-sections on the Be, B+, C2+, N3+, O4+, Ne6+, Fe22+ and U88+ atomic targets, in the beryllium isoelectronic sequence (BIS), are calculated using the modified versions of simplified improved binary-encounter dipole model (siBED) [W.M. Huo, Phys. Rev. A 64 (2001) 042719]. The modified models, QIBED (with the ionic correction) and RQIBED (with both the ionic and relativistic corrections) [M.A. Uddin, A.K.F. Haque, A.K. Basak, B.C. Saha, Phys. Rev. A 70 (2004) 032706], are found to provide an excellent description of the experimental data for all the targets in BIS with the same generic values of the two parameters and in the models. The RQIBED results describe satisfactorily the assessed data of Be and its predictions for U88+ account for well the experimental K-shell ionization data of Sn, with almost the same properties of the ionized orbit concerned, even up to around 2 MeV. [Copyright &y& Elsevier]

One ionization mechanism of barium ions is the resonant excitation of a 3d inner-shell electron with the subsequent decay of the resulting highly excited intermediate state by multiple autoionization processes. We have experimentally studied this process by observing associated resonance structures – in the energy range 700–800 eV – in the multiple (up to sevenfold) ionization cross-sections of Baq+ ions with 1&les;q&les;13. The 3d-resonance strength is determined quantitatively as a function of initial and final ion charge state. The results suggest a statistical description of multiple ionization via the excitation of inner-shell electrons. [Copyright &y& Elsevier]

We measured absolute cross-sections for the electron-impact ionization and dissociative ionization of the three nitrogen–oxygen compounds NO, NO2, and N2O from threshold to 200 eV using the fast-neutral-beam technique. In spite of the importance of these molecules in combustion, low-temperature plasmas, pollution control, and planetary atmospheres, the database of absolute total and partial electron-impact ionization cross-sections for these species is not very comprehensive and existing data reveal some discrepancies. To the best of our knowledge, this is the first time that absolute partial ionization cross-sections for all three species have been measured by the same group using the same experimental technique and apparatus. Comparisons with other available measured and calculated ionization cross-section data are made. [Copyright &y& Elsevier]