Ionization of M subshells of Pb atoms by electron impact in an energy range of 5–30 keV

The relative intensities of the M ₅ N and M ₄ N satellites of Pb under electron bombardment of thick targets in the range of accelerating voltages U = 5?30 kV are experimentally investigated. Based on the previously proposed model of M X-ray emission, the relative intensities of these satellites are calculated using the total ionization cross sections of M subshells under electron impact found in different approximations. It is established that, among the models yielding analytical expressions for calculating total ionization cross sections, the model of classical binary collisions provides the best agreement with experimental data in the electron energy range under study. The parameters of the semiempirical Bethe formula for calculating the ionization cross sections of Pb M subshells under electron impact are determined.     

Electron impact ionization cross sections of the CO2 clusters

The modified Jain–Khare semi-empirical formalism for the evaluation of differential and integral electron impact ionization cross sections for molecules has been extended to the evaluation of cross sections for the electron ionization of CO₂ clusters: (CO₂)₂₄₀ and (CO₂)₁₇₀₀. The energy dependent differential cross sections are evaluated at the incident electron energies of 50, 100 and 200 eV. The integral total ionization cross sections have been calculated in the energy range varying from ionization thresholds to 1000 eV which revealed a good agreement with the available experimental and the theoretical data. The ionization rate coefficients have also been evaluated using the presently calculated ionization cross sections and Maxwell–Boltzmann energy distributions.     

Relative intensities in X-ray photoelectron spectra: Part XI. Calculation of photoionization cross sections for valence levels of SiF4

Partial photoionization cross sections for valence MOs of SiF₄ have been calculated by the method of multiple scattering with atomic amplitudes (MSAA) for excitation energies ranging from the ionization threshold to 60 eV. The cross section behavior near the ionization thresholds is determined mainly by the shape resonances of t₂ and e symmetries. The resonance structure of photoionization cross sections is treated in terms of deviations from the additive model, and of conceptions of “quasi-stationary” states and “quasi-forbidden” bands. The energy positions of quasi-stationary states in SiF₄ are compared with the data obtained from X-ray absorption spectra. The dependence of theoretical cross sections on the inter-nuclear distances is studied.     

Single and double ionization of neon 2s- and 2p-subshells by proton and electron impact

Absolute single and double ionization cross sections of neon 2s- and 2p-subshells for proton (40–900 keV) and electron impact (0.2–10 keV) have been measured using photon spectroscopy in the spectral range of the vacuum ultraviolet. Cross sections for double ionization decrease more rapidly with increasing impact energy than cross sections for single ionization. No definite asymptotic energy dependence of a Bethe-Fano-plot could be found for double ionization in contrast to single ionization. The experimental results are compared with theoretical predictions of the shake-off model and Gryzinski's classical binary encounter theory. Better agreement is found with the latter, indicating that successive binary collisions have to be considered as a strong mechanism for double ionization by protons or electrons of the investigated energy range. Comparison is made with other experimental results for double ionization by photon impact or capture ionization by proton impact.     

Multielectron ionization of atoms by fast ions: An approximation by normalized exponentials

Multielectron ionization of neutral atoms by fast positive ions is considered in terms of the independent particle model. A relatively simple technique for calculating the multielectron ionization probabilities and cross sections through the impact parameter is suggested in which one-electron ionization probabilities are represented as normalized exponentials p _nl(b) = p _nl(b) = p _nl(0)exp(?α_nl b), where b is the impact parameter and n and l are quantum numbers of the target atomic shell. Exponent α_nl is determined from the Born one-electron ionization cross section for target atoms, and preexponential p _nl(0) (the ionization probability at a zero impact parameter) is found from a geometrical model. This technique provides the normalization condition p _nl(b) ≤ 1 irrespective of the velocity and charge of striking ions and makes it possible to calculate the one-, two-, and three-electron ionization cross sections, which, when added up, make a major contribution to the total cross section, up to a factor of 2. The results of our computations are compared with experimental data and analytical results of other authors.     

Electron impact ionization of SiCl<Subscript>2</Subscript> and SiCl

We measured absolute partial cross sections for the formation of all singly charged positive ions produced by electron impact on SiCl₂ and SiCl from threshold to 200 eV using the fast-neutral-beam technique. Some of the cross section curves exhibit an unusual energy dependence with a pronounced low-energy maximum at an energy around 30 eV, which may be indicative of the presence of indirect ionization channels. Dissociative ionization channels are dominant for both species. The experimentally determined total single ionization cross sections for both species agree very well with calculated cross sections using the Deutsch-M?rk (DM) formalism. A brief summary of the ionization cross sections determined for all four SiCl_x (x=1–4) species is given highlighting similarities and differences.     

Structure and thermal stability of AgCu chiral nanoparticles

Theoretical studies of electron impact double ionization cross sections of Ne⁵⁺ and Ne⁶⁺ ions have been performed in the binary encounter approximation (BEA). Direct double ionization (DDI) has been investigated in the modified double binary encounter model. The K-shell ionization cross sections have been also calculated in the BEA to take into account the contributions to double ionization from the ionization-autoionization (IA) process. The effect of the Coulombic field of the target ion on the incident electron has been considered in the present work. Accurate expression of σ _ΔE (cross section for energy transfer ΔE) and the Hartree-Fock (HF) velocity distributions for the target electrons have been used throughout the calculations. The present results are in overall moderate agreement with the experimental observations. Possible reasons behind the discrepancies between the theory and the experiment have been discussed.     

Electron ionization cross sections for neutral fullerene C70

The energy dependent ionization cross sections corresponding to the formation of singly, doubly and triply charged cations in the electron impact ionization of C₇₀ are evaluated employing a semiempirical formulation at the incident electron energies of 100 and 200 eV. The integral ionization cross sections have also been calculated in the energy range varying from ionization thresholds to 1000 eV which revealed a satisfactory agreement with the available experimental and the theoretical data. The ionization rate coefficients corresponding to the various cations have also been evaluated using the presently calculated ionization cross sections and Maxwell-Boltzmann energy distributions.     

Ionization function of magnesium for electron impact

Ionization cross sections for electron impact are measured with crossed beams of Mg atoms and pulsed electrons. Total numbers of particles are determined by the light emission of excited atoms. The ionization cross section obtained for electron energies from 7 eV to 60 eV has its maximum valueq _i (max)=7.8 · 10^?16 cm² at 12 eV electron energy.     

Inner-shell ionization ofZ=25–32 elements by 5-48 MeV32S ions

TheK-shell ionization cross sections of Mn, Ni, Cu, Zn and Ge under³²S bombardment have been measured in the energy range from 5 to 48 MeV. The cross sections are compared with available theories based on a direct Coulomb ionization mechanism and with the predictions of theK-vacancy sharing process. This last process can reasonably account for the measured cross sections at high bombarding energies. The energy shifts of theK _α- andK _β-lines and theK _α/K _β-intensity ratios have also been measured. This information is used to deduce the defect configuration of the atoms. The mechanisms responsible for the multiple vacancy production are discussed.     

Absolute electron impactK-ionization cross sections of titanium and nickel (≦50 keV)

The absoluteK-ionization cross sections of Ti and Ni by electron impact (impact energy ≦50 keV) was measured detecting the X-rays emitted by thin solid film targets of known mass thickness with a flow proportional counter. The experimental method, especially the correction procedures and the measurements are described, the results compared with calculations in different theoretical approaches. For impact energies aboveE ₀/E _K>1.5 (E _K=K-shell ionization energy) a systematic deviation of about +20% occurs in comparison with the best agreeing calculations of M.R.H. Rudge and S.B. Schwartz. A fit to Drawin's empirical formula reveals that the measurements are approximated better than ±10 % within the range of comparison.     

H<Superscript>+</Superscript><Emphasis Type="Bold">and He</Emphasis><Superscript>2+</Superscript> impact single and double ionization of lead

H⁺ and He²⁺ impact single and double ionization cross sections of ground state lead atoms have been calculated in the binary encounter approximation. Calculations of direct double ionization cross sections have been performed in the modified double binary encounter model. The accurate expressions of σ_ΔE (cross-section for energy transfer ΔE) and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. Contributions to double ionization from Auger effect following ionization of inner shells have been considered in the present work. Our H⁺ impact single and double ionization cross sections are in good agreement with the experimental observations. In calculations of He²⁺ impact cross sections, the present theoretical approach shows limited success in the experimentally investigated region (50–350 keV amu^-1).     

K-shell X-ray production for fluorine ions on target elements Ti to La

The production of target atomK-shell X-rays has been studied for 2 to 28 MeV fluorine ions incident on thin solid targets of 14 elements with atomic numbers Z₂=22 to 57. Total X-ray production cross sections, energy shifts ofK _α andK _β lines andK _α/K _β intensity ratios were measured with a Si(Li) detector. The results of cross section measurements are compared with theoretical predictions of inner shell ionization. In most cases, satisfactory agreement between measured cross sections and theoretical Coulomb ionization cross sections, corrected for the perturbation of the target atom by the projectile charge and for relativistic effects, was obtained.     

Excitation and photoionization processes involving the bound ns electrons

We have considered the processes of excitation and ionization of light multicharged ions by impact of high-energy particles, which proceed with participation of the ns electrons. The screening corrections to the energy levels and photoionization cross sections are evaluated analytically within the framework of the non-relativistic perturbation theory with respect to the electron-electron interaction. The universal scalings for the excitation and ionization cross sections are studied for arbitrary principal quantum numbers n.     

Total cross sections for electron scattering from well-known and exotic molecules

In this review paper, scattering of intermediate to high energy electrons on well-known as well as exotic molecular targets is considered. The ‘additivity rule’ and its modifications for calculating various total cross sections are discussed against the background of an extensive experimental data. The theory succeeds at high impact energies (E _i>100 eV). Tentative upper and lower limits of e-molecule ionization cross sections are identified. Fitting formulas to represent total cross sections as functions of energy are also given.     

Oxygen inducedK-shell ionization of selected elements from sulphur to bromine

K-shell X-ray production cross sections for oxygen ions on thin solid targets of 13 selected elements with atomic numbers between 16 and 35 were measured by a Si(Li) detector at incident ion energies from 7 to 24 MeV. Ionization cross sections are compared with calculations assuming Coulomb-ionization. Best agreement is found with theoretical cross sections that include corrections for binding energy and Coulomb deflection effects. Energy shifts ofK _α andK _β X-rays andK _α /K _β intensity ratios were also measured and are used to deduce information about outer shell ionization.     

K-shell ionization of Si,Ti, Cu and Ag for incident protons,4He and14N ions in the energy range of 0.17–2.0 MeV/amu

K-shell X-ray production cross sections of Si, Ti, Cu and Ag were measured for incident protons,⁴He and¹⁴N ions in the energy range of 0.17≦E ₁/A ₁≦2 MeV/amu. The experimental ionization cross sections are compared with calculations according to the simple Plane Wave Born Approximation (PWBA) theory as well as the corrected PWBA model (PWBABC). Strong deviations of the experimental cross sections from theZ ₂ ¹ scaling are observed and discussed quantitatively.     

Electron impact ionization of positive ions

A binary encounter model with Vriens' expression for σ_ΔE and quantum mechanical velocity distribution for the bound electron has been used to calculate electron impact ionization cross sections for ions. The calculated cross sections agree well with experimental observations.     

About the effect of a bound state on ionization cross sections in ion-atom collisions

The cross sections σ_nl for ionization of hydrogen-like ions by heavy particles from the nl = 3s, 3p, 3d, 4s and 4p states have been calculated in the Born approximation. A structure in the energy dependence of the cross sections σ_nl and the ratios of the cross sections σ_nl/σ_1s due to the radial wave function of a bound state is discussed.     

Multiple ionization and the charge state evolution of ions exposed to electron impact

Charge state abundances of atoms exposed to an electron flux for a time t are calculated from experimental cross sections by considering either electron impact single ionization only or by including multiple ionization. When multiple ionization is neglected Xe^q+ ion abundances (q = 0,1,…,6) for an electron energy of 700 eV are off by a factor of up to 2 both in peak size and in time necessary to reach the peak value.