Modified over-barrier model for ionization cross sections of atomic hydrogen by multiply charged ions

The impact ionization of atomic hydrogen in collisions with H⁺, He²⁺, Li2,3+, C2,3,4,5,6+, N2,3,4,5+, O2,3,4,5,6+, and Ar3,4,5,6+ ions has been studied by the modified over-barrier model at low-to-intermediate velocities. Compared with the calculated results of the classical trajectory Monte Carlo (CTMC) method and the unitarized-distorted-wave approximation (UDWA), this model satisfactorily reproduces the experimentally obtained velocity dependence of the absolute ionization cross sections at intermediate impact velocities.     

Electron scattering with LiH molecule including a realistic dipole potential

Various electron scattering processes are examined theoretically for the strongly polar lithium hydride molecule. We have introduced a realistic dipole potential to calculate rotational cross sections of LiH upon electron impact. From the ionization threshold onwards total cross sections for elastic and inelastic scattering are evaluated in the complex molecular potential, and total ionization cross sections are extracted by CSP-ic method developed in recent years. While most of the results are new some indirect comparisons are made to draw conclusions.     

Simple model for the ionization of helium atoms by fully and partially stripped ions in the strong interaction region

Theoretical calculations employing the modified over-barrier model to investigate single and double ionization cross sections of helium in collisions with highly charged ions are presented in the strong perturbation region. It shows the velocity and charge state dependences of cross sections, which coincides with the available experimental data. In order to determine the reliability of this model for partially stripped projectiles, the cross-section ratios have been measured for CZp+, OZp+-He (Zp=1-4) by the coincidence technique in the velocity range of 1-4.5 a.u. The calculated results are approximately in agreement with the experimental data.     

Positron scattering from alkaline-earth elements

The total (elastic + inelastic) cross sections fore ⁺ impact on alkaline-earth elements from Be to Ra are calculated by employing a complex spherical optical potential. This potential has static, polarization and absorption components. The positron energy range is from a few eV to several thousand eV. We have compared our elastic cross sections for Mg and Ca with the other available results and the agreement is good for energies above 100eV. We have also compared our absorption cross sections withe ⁻ ionization cross sections at high energies where our absorption cross sections are in good accord. We have made Bethe plots fore ⁺ scattering on these elements.     

Projectile electron loss in collisions of light charged ions with helium

We investigate the single-electron loss processes of light charged ions （Li^1＋,2＋, C^2＋,3＋,5＋, and O^2＋,3＋） in collisions with helium. To better understand the experimental results, we propose a theoretical model to calculate the cross section of projectile electron loss. In this model, an ionization radius of the incident ion was defined under the classical over-barrier model, and we developed ＂strings＂ to explain the processes of projectile electron loss, which is similar with the molecular over-barrier model. Theoretical calculations are in good agreement with the experimental results for the cross section of single-electron loss and the ratio of double-to-single ionization of helium associated with one-electron loss.     

Stereo-dynamical ion-pair formation in collisions of highly-charged ions with argon dimers

Multiple ionization process of a rare gas dimer BC collided with a slow highly charged ion A^q+ is investigated with the three-center Coulombic over-barrier model previously developed by the present authors. To reveal stereodynamical effects, we calculate asymmetric ion-pair formation cross sections σ(Q_B,Q_C) as a function of the orientation angle. We introduce a pair of atomic impact parameters b_B and b_C with which we distinguish the near and far sites. Furthermore, we distinguish the forward and backward emitted ions produced as a result of Coulomb explosion. Partial screening effects are also considered.     

Positron scattering and ionization of neon atoms—theoretical investigations

Although positron scattering with inert gas atoms has been studied in theory as well as in experiment, there are discrepancies. The present work reports all the major total cross sections of e+-neon scattering at incident energies above ionization threshold, originating from a complex potential formalism. Elastic and cumulative inelastic scatterings are treated in the complex spherical e+-atom potential. Our total inelastic cross section includes positronium formation together with ionization and excitation channels in Ne. Because of the Ps formation channel it is difficult to separate out ionization cross sections from the total inelastic cross sections. An approximate method similar to electron-atom scattering has been applied to bifurcate ionization and cumulative excitation cross sections at energies from threshold to 2000 eV. Comparisons of present results with available data are made. An important outcome of this work is the relative contribution of different scattering processes, which we have shown by a bar-chart at the ionization peak.     

Charge transfer in the collision system He<Superscript>2+</Superscript> + C<Stack><Subscript>60</Subscript><Superscript>+</Superscript></Stack>: Theory and experiment

Fullerenes are a direct link between atoms with discrete electronic energy levels and solids with a band structure and a well-defined surface. In this paper, we report on a quantum mechanical treatment of charge transfer and ionization in the ion-ion collision system ³He²⁺ + C ₆₀ ⁺ . This approach considers under- and over-barrier transitions through the one-dimensional barrier between the collision partners. The calculated cross sections for charge transfer compare favorably with experimental data measured in the center-of-mass energy range from 27 to 196 keV employing the crossed beams technique.     

Coupled-channel optical calculation for positron—lithium scattering

Positron scattering with atomic lithium is investigated by using a coupled-channel optical method.The ionization continuum and positronium formation channels are taken into account via a complex equivalent-local optical potential.The positronium formation cross sections and the ionization cross sections,as well as the total scattering cross sections,are reported at energies above 3 eV and compared with available experimental and theoretical data.     

Complex scattering potential – ionization contribution (CSP-ic) method for calculating total ionization cross sections on electron impact

In this article, we report calculations of total ionization cross sections, Q _ion , for simple atoms (C, N, O, F) and molecules (NO and NH₃)_{3}) of atmospheric interest on electron impact at energies from threshold to 2000 eV. We have employed the complex scattering potential – ionization contribution (CSP-ic) method for the present study. Attempt has been made to improve the method by computing the parameter that involves the ratio of sum of the total excitation cross sections (Σ Q _exc ) and total inelastic cross section (Q _inel ) at the peak of the inelastic cross section. The present study not only provided a better estimation of the parameter involved in the CSP-ic method but also provided better agreement with the available experimental and theoretical data on the ionization cross sections of the simple atomic and molecular targets studied here.     

Helium ionization with excitation of the atom accompanied by absorption and scattering of high-energy photons

We calculate analytically the cross sections for ionization of the helium atom with absorption and scattering of high-energy photons. The electrons are assumed to be moving in the Coulomb field of the nucleus. The electron-electron interaction is taken into account in the first order of perturbation theory. The high-frequency limits for the ratios of these cross sections to the single-electron ionization cross sections are obtained for s-excitations in absorption and for s-and p-excitations in scattering. Zh. éksp. Teor. Fiz. 111, 862–870 (March 1997)     

Calculation of Absolute Outer-Shell Electron Impact Ionization Cross Sections

The recently developed semiempirical DM-approach for the calculation of electron impact single ionization cross sections is applied here to the ionization of the rare gases (Ne, Ar, Kr and Xe) via ejection of an outer s-shell electron. The results obtained are compared with previous experimental and theoretical s-shell ionization cross section functions.     

Single electron loss in the collisions of C3 + and atomic hydrogen

This paper studies the projectile electron loss cross sections of C3+ colliding with atomic hydrogen in the frame work of extended over-barrier model at intermediate velocities (25 keV/u-600 keV/u). The electron loss is calculated in terms of the interaction between the screened target nucleus and the active projectile electron and of the interaction between projectile electron and target electron. Compared with the convergent close-coupling calculations, screening and anti-screening calculations, this model satisfactorily reproduces the experimentally obtained energy dependence of the electron-impact ionisation cross sections and the single electron loss cross sections over the energy range investigated here.     

Ionization of heavy ions in relativistic collisions with neutral atoms

The problem of ionization of ions in ion-ion and ion-neutral relativistic collisions is considered. Formulas for ionization cross sections are derived in the Born approximation in terms of the momentum transfer without allowance for magnetic interactions. Using these formulas implemented in the LOSS-R code, the ionization cross sections are calculated for the K shells of neutral atoms colliding with protons and also for 1s and 2p electrons of multiply charged heavy ions (nuclear charge Z = 80−90) colliding with bare nuclei and neutral atoms. The calculation results are compared with experimental data and calculations of other authors.     

New semi‐empirical formulas for calculation of K‐shell ionization cross sections of elements from beryllium to uranium by proton impact

Experimental ionization cross sections for K‐shell by protons in target atoms from beryllium to uranium available in the literature from 1953 to 1999 (nearly 5400 values) are collected to deduce the semi‐empirical K‐shell ionization cross sections by fitting the experimental data normalized to their corresponding theoretical values based on the ECPSSR model which accounts for Coulomb deflection, Energy loss of the projectile, Perturbed Stationary State and Relativistic effects, as a function of the reduced velocity parameter. Our results are compared with the experimental data and with the ECPSSR values and reference ionization cross sections obtained by Paul and Sacher [H. Paul and J. Sacher, At. Data. Nucl. Data. Tables 1989 , 42, 105]. Copyright © 2010 John Wiley & Sons, Ltd.     

Photoionization of the excited He atom in Debye plasmas

We present theoretical photoionization cross sections for He 1s2s ¹S and He 1s2p ¹P states in a Debye plasma environment by the complex coordinate rotation method, using a finite L² basis set constructed from one electron Laguerre orbitals. The plasma environment is found to appreciably influence the photoionization cross sections near the ionization threshold. In this regard, the photoionization cross sections of isolated He are compared with other theoretical and experimental results. Our results are in good agreement with the previous results. A new minimum appears in the photoionization cross section curve for the metastable 1s2s ¹S state. Results are given for the S- and D-wave partial photoionization for the excited 1s2p ¹P state.     

Measurements of K-shell ionization cross sections of35Br,37Rb,39Y using low energy protons

K-shell ionization cross section measurements are reported for₃₅Br,₃₇Rb and₃₉Y targets caused by protons over 300–400 keV energy range in 20 keV increment. The K-shell ionization cross sections (σ _k ^l ) at different energies were deduced from the K_α and K_β X-ray production cross sections which were obtained from X-ray yields of the K_α and K_β transitions. The experimental values are compared with the calculated values of ECPSSR theory and empirical reference cross sections. The resultant K-shell ionization cross sections are found to be in reasonable agreement with the ECPSSR theory. The K_α/K_β intensity ratios are also presented and compared with other experimental values and also with the theoretical one-hole values given by Scofield.     

Electron impact single ionization of copper

Electron impact single ionization cross sections of copper have been calculated in the binary encounter approximation using accurate expression for σ _ΔE as given by Vriens and Hartree-Fock momentum distribution for the target electron. The BEA calculation based on the usual procedure does not show satisfactory agreement with experiment in this case but a striking modification is found to be successful in explaining the experimental observations. The discrepancy is linked with the ionization of the 3d ¹⁰ electrons and probably effective single ionization does not take place from 3d shell of copper leading to smaller values of experimental cross sections.     

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.     

Momentum-space calculation of electron-CO elastic collision

We report a momentum-space study on low-energy electron-CO collisions.Elastic differential cross sections(DCS) are obtained using a static-exchange-optical(SEO) model for the incident energies of 2,3,5,and 10 eV.Polarization effect of higher reaction channels,including the ionization continuum,on the elastic collision is represented by an ab initio equivalent-local optical potential.The cross sections are compared with experimental measurements and other theoretical results.