Excitation of Autoionization States and Electronic Stopping Powers at Collisions of Slow Ions with a Solid

It has been shown that the excitation of autoionization states at collisions of keV ions with a solid is decisive for inelastic energy loss and, correspondingly, the electronic stopping power dE/dx. It has been proposed to estimate the electronic stopping power dE/dx using the relation of cross sections for the excitation of autoionization states to ionization cross sections. When ionization cross sections are unknown, scaling is used to calculate ionization cross sections at the excitation of the L and M shells. A threshold dependence of the electronic stopping power dE/dx on the energy of bombarding ions has been predicted.     

Cross sections of inelastic processes in collisions between relativistic structured heavy ions and atoms

A nonperturbative method is developed for the calculation of cross sections of inelastic processes in collisions between structured high-charge heavy ions moving at relativistic velocities and atoms. By structure ions are meant partly stripped ions consisting of an ion nucleus and a number of bound electrons which partly compensate the core charge and form the electron “coat” of the ion. The single ionization cross section of hydrogen atom and single and double ionization cross sections of helium atom are calculated. It is demonstrated that the inclusion of the extent of ion charge may bring about a marked variation of the respective cross sections compared to ionization by point ions of the same charge and energy.     

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.     

Ionization,charge exchange,and excitation during collisions of sodium ions with argon

The absolute values of cross sections of ionization, charge exchange, and excitation during Na⁺-Ar collisions are measured in the ion energy range 0.5–10.0 keV. Experiments are performed by a modified method of transverse electric field and by the optical spectrometry method. The mechanisms for realization of inelastic channels are explained qualitatively on the basis of a schematic correlation diagram of diabatic quasi-molecular energy levels of a system of colliding particles. The quasi-molecular nature of interaction is revealed for excitation processes. The excitation mechanisms of collision partners are established. A noticeable contribution to the excitation of the 4s state of the argon atom comes from the cascade transition from upper-lying 4p and 3d levels. An oscillatory structure is observed in the excitation functions of atomic lines of ArI (104.8 and 106.7 nm). The shape of the curve describing the dependence of the charge-exchange cross section on the collision energy is explained by the presence of two nonadiabaticity regions. In the low-energy region (up to E = 2 keV), charge exchange is due to electron capture to the ground state as a result of Σ–Σ transitions, while Σ–Π transitions associated with the rotation of internuclear axis play the leading role in charge exchange in the energy range E > 3 keV. The contribution of a number of inelastic channel is estimated for the ionization process. It is found that the main contribution to ionization is associated with the decay of self-ionization states in an isolated atom.     

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.     

Resonant inelastic contact scattering of X-ray photons on atoms and ions

The existence of an extended resonance structure outside the X-ray emission regions is theoretically predicted in the total double differential cross section for the scattering of linearly polarized photons on free atoms (ions). This structure is almost entirely determined by inelastic photon scattering of the contact type. The amplitude of the inelastic contact scattering probability is described using an analytical expression for a non-relativistic transition operator, which was previously obtained by the author outside the dipole and momentum approximations. The resonant inelastic contact scattering of X-ray photons on a neon atom and neonlike ions of argon, titanium, and iron has been studied. Calculations were performed in a nonrelativistic approximation for the wave functions of the scattering states, with allowance for many-body effects of the radial relaxation of one-electron orbitals in the Hartree-Fock field of a deep 1s vacancy and (for neon atom) the double excitation/ionization of the ground atomic state.     

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)     

Inelastic scattering of heavy ions at intermediate energies with excitations of nuclear collective states

Excitation of low-lying nuclear collective states upon scattering of heavy ions with energies of several tens of MeV/nucleon has been studied. The interaction potential leading to excitation is chosen in the form of a derivative of the microscopic (or semimicroscopic) nucleus-nucleus double-folding optical potential. Elastic and inelastic scattering cross sections have been calculated within the high-energy approximation; the inelastic scattering amplitude was obtained in the first order in the deformation parameter. The cross sections are compared with the experimental data on scattering of ¹⁷O from a series of nuclei with excitation of the 2⁺ level.     

Ionization in Ps–H scattering

Coulomb–Born approximation has been used to study three different types of ionization in positronium (Ps) and hydrogen scattering. The present Ps–H system contains four centers; we have considered all the Coulomb interactions and neglected exchange assuming the fact that at relatively higher energies above thresholds, the effect of exchange is not so important. All the important target elastic and inelastic channels are included. The non-unitarity problem in the target elastic channels, discussed by McAlinden et al. in 1996 in their positronium–atom scattering studies is overcomed in the present calculation using the orthonormality properties of target wavefunctions and a simple algebra. Comparative studies are made among ionization cross sections with different target excitations and different Ps-excitations together with summed Ps-ionization, summed H-ionization, both-ionization, summed excitation, total ionization and total cross sections. The present Letter indicates the importance of all the three different types of ionization and the importance of target elastic channels in Ps–H scattering.     

Ionization-Excitation of helium-like ions by high-energy electrons

The differential and total cross sections are calculated for the ionization of helium-like ions that is accompanied by the excitation of residual ions to ns states owing to an electron impact. Nonrelativistic perturbation theory in electron–electron interaction with Coulomb functions used for a zero-order approximation underlies these calculations. The expressions obtained in this way have a universal character. They are applicable at moderate values of the target charge number Z and high energies of incident electrons. A comparison with total cross sections calculated for the helium atom within various theoretical approaches is performed.     

Emission of an atom during its interaction with an ultrashort pulse of electromagnetic field

The electronic transitions and emission of an atom during its interaction with a spatially inhomogeneous ultrashort pulse of electromagnetic field are considered. The probabilities of excitation and ionization, as well as the spectra and cross sections of reemission of such a pulse by the atom, are obtained. As an example, the one-and two-electron inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-and helium-like atoms are considered.     

Direct numerical reconstruction of inelastic cross sections from REELS and ISS spectra

The reconstruction of inelastic scattering cross sections faces two problems: the measured signal (energy spectrum) is a multiple scattering signal; the inelastic energy loss is nonuniform over the target depth. In this paper, we present a method for numerical reconstruction of cross sections from characteristic energy loss spectra, which efficiently solves both problems within a multilayer model. It is shown that the inverse problem of cross section extraction in the three-layer model is ill-conditioned, and the method is practically inapplicable to the three-layer model. The direct numerical reconstruction method yields a strongly “noised” result and can be applied only to obtain a priori information on the inelastic cross section form for further fitting. Using a combination of two methods, inelastic scattering cross sections were reconstructed for aluminum from characteristic energy loss spectra at probe beam energies of 5 and 40 keV. It is shown that ionization in solids should be described as a local process and as a collective one using the dispersion formula similarly to the case of excitation plasmons.     

Two-electron transitions in collisions of fast multiply-charged ions with helium-like atoms

Single and double excitation and ionization of a helium-like atom are considered based on the eikonal approximation. Simple analytical formulas are derived for the cross sections of inelastic collision. A comparison with the experiment is conducted. Scientific Research Institute of Applied Physics at Tashkent State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 44–48, February, 2000.     

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.     

类钠离子的电子碰撞电离截面

利用相对论修正扭曲波玻恩交换近似,计算了8个类钠离子的电子碰撞直接电离和激发自电离截面.基于这些结果,给出了计算类钠等电子系离子(18≤Z≤39)直接电离和激发自电离截面的高精度拟合公式.计算结果与现有的实验值和其他理论值比较,相当一致 关键词： 电离截面 组态相互作用 扭曲波玻恩交换近似 拟合公式     

电子与多电荷离子的碰撞电离(英文)

主要揭示了不同电离机制对高电荷态离子单电离和多重电离的贡献 ,包括直接电离 (一步过程 )、激发 自电离 (两步过程 )以及内壳Auger过程 ,研究了高电荷态镨离子的电子碰撞电离. Electron-impact ionization of ions is one of the most fundamental processes in every kind of plasma. Especially in high-temperature plasmas-whether in laboratory (nuclear fusion) or in astrophysics (atmosphere of stars)-atoms become ionized into multiply-charged ions by electron impact. The main purpose of our investigations is to unravel the contributions from different ionization mechanisms-like direct ionization (one-step process), excitation-autoionization (two-step process) and...     

Inelastic scattering of broadband electron wave packets driven by an intense midinfrared laser field

Intense, 100 fs laser pulses at 3.2 and 3.6 μm are used to generate, by multiphoton ionization, broadband wave packets with up to 400 eV of kinetic energy and charge states up to Xe(+6). The multiple ionization pathways are well described by a white electron wave packet and field-free inelastic cross sections, averaged over the intensity-dependent energy distribution for (e, ne) electron impact ionization. The analysis also suggests a contribution from a 4d core excitation, or giant resonance, in xenon.     

Ne+离子与Li原子碰撞过程中激发态的研究

本文通过观测Ne⁺离子与Li原子碰撞中的发射谱,对碰撞中的电子俘获和靶激发过程进行了研究。在可见光范围给出了所观察到的各条谱线的发射截面及相应上能级的激发截面。对电子俘获过程与能量亏损和靶原了电离势的关系进行了讨论。Ne⁺离子能量范围为20—150keV 关键词：     

含温有界原子模型下电子与离子碰撞激发和电离截面的理论研究

采用扭曲波玻恩交换近似方法，在自由原子模型下计算了电子与离子碰撞激发、电离截面，计算值与实验一致；在含温有界平均原子模型下，系统研究了不同温度、密度等离子体中离子的电子碰撞直接电离截面，发现由于温度、密度效应导致离子的能级漂移，引起等离子体中离子的碰撞电离截面比自由原子情形发生较大变化. 关键词： 平均原子模型 扭曲波波恩交换近似 电离截面     

Double ionization and excitation ionization in the Compton scattering of high-energy photons for metastable states of heliumlike ions

Double ionization and excitation ionization in Compton scattering for heliumlike ions in metastable states are investigated. The electron energy distribution for double ionization and the total cross sections for both processes are calculated. The calculations are carried out in the zeroth order of perturbation theory with respect to electron-electron interaction, using Coulomb wave functions as the first approximation. The resulting equations are valid only in the high-energy nonrelativistic range. It is assumed that Z≫1, but αZ≪1 (Z is the charge of the nucleus, and α is the fine-structure constant). Zh. éksp. Teor. Fiz. 116, 1889–1902 (December 1999)