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Cross section versus electron energy for hydrogen-like ions and atomic hydrogen, ( a ) shows H(1S) (Shah et al 1987, dots), He + (Peart et al 1969, down triangles), Li 2 + (Tinschert
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For the first time absolute cross sections for electron impact ionization of the hydrogen-like ions B4+, C5+, N6+ and O7+ at electron energies from below threshold up to about 6 keV have been measured using the crossed-beams technique. All measured cross sections are in very good agreement with available distorted-wave exchange calculations and the...
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... 1 . 0278 + Z − 1 in units of the binding energy I H = 13 . 6 eV of hydrogen and the area defined by Bohr’s radius a 0 = 0 . 5 × 10 − 8 cm. With the help of these scaling functions and the cross section of (5) it is possible to predict any direct ionization cross section along the isoelectronic sequence accurately as can be seen in figure 8. As expected the cross section for hydrogen ( Z = 1) shows the largest deviation from the simple form (5) of the cross section. All targets of Z 2 are well described. Within the framework discussed above, the ionization process of hydrogen-like ions is well understood. However, the scaling laws as well as the ionization shape (5) no longer hold for highly charged hydrogen-like ions. It has been pointed out that significant changes will occur when the atomic number increases to Z = 54 or even to Z = 92 (Tinschert et al 1989). Relativistic effects gain influence on the cross sections for electron impact ionization of high- Z ions. In this Z -region, no absolute cross section measurements exist. Claytor et al (1988) and Marrs et al (1994) measured relative cross sections for U 91 + ions with large experimental uncertainties. Crossed-beams experiments can provide accurate absolute cross sections for electron impact ionization of highly charged hydrogen-like ions. These data would improve our understanding of relativistic effects in electron impact ionization of ions in general and in the scaling behaviour for hydrogenic species in particular. For the first time absolute cross sections for the ionization of hydrogen-like B , C , N 6 + and O 7 + ions were measured employing the animated crossed-beams technique. The database on hydrogen-like multiply charged ions was extended by this experiment and the results are in good agreement with indirect measurements and theoretical calculations. In spite of the good accuracy of the measurement none of the calculations presented in this paper disagrees within the small experimental errors with the data in the investigated range of impact energies E and nuclear charges Z . An extension of the classical scaling law has allowed us to provide all non-relativistic electron impact ionization cross sections of hydrogen-like ions in closed form to an accuracy well within the experimental errors. A deeper understanding of relativistic effects requires a further extension of the database to hydrogen-like ions of higher Z numbers. Support by the Deutsche Forschungsgemeinschaft (DFG), Bonn-Bad Godesberg, is gratefully acknowledged. The authors thank Dr F Melchert for helpful discussions. The authors from the University of Freiburg also acknowledge support by the DFG, within the Sonderforschungsbereich 276 and through the Gerhard ...
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... This explanation assumes that the Fig. 1, except for the Li 2+ target with the experimental data due to Tinschert et al. [25]. Fig. 1, except for the B 4+ target with the experimental data due to Aichele et al. [27]. direct and exchange components are of a similar sign. ...
Electron-impact excitation and ionization of H-like ions of nuclear charge Z=2,⋯,8 have been calculated from thresholds to high energies, with a particular focus on spin asymmetry of the cross sections. It is found that the importance of electron exchange is undiminished with increasing Z. Away from resonance regions, scaling considerations allow for accurate nonrelativistic estimates of the total-electron-spin-dependent cross sections for Z>8.
... Scaling properties and the deduction of universal crosssection shape functions for the ionization of atomic targets can be used to predict cross sections for electron-impact single or even multiple ionization. Scaling rules have been discussed by Aichele et al. [8] in connection with ionization of hydrogenlike ions. Their application of the analytical parametrization of the shape of atomic ionization cross sections proposed by Rost and Pattard [9] shows excellent agreement with the available experimental data. ...
Electron-impact single-ionization cross sections for the W5+ ion have been studied experimentally and theoretically. Measurements of a detailed ionization spectrum and of absolute cross sections were performed employing the crossed-beams method in the energy range from the ionization onset up to 1000 eV. The experimental data show a prominent contribution of W5+ ions in metastable states. The theoretical analysis
includes level-to-level calculations from the 4 f145s25p65d ground configuration and long-lived levels of the 6s, 5p55d2, 4f135d2, and 4f135d 6s configurations. Direct-ionization and excitation-autoionization contributions to the total single-ionization cross sections were calculated employing a distorted-wave approximation. Radiative
damping was taken into account. It is shown that correlation effects play an important role and lead to substantial reduction of cross sections. Theory and experiment are in quite good agreement when, within a statistical model, a (85± 9)% fraction of parent ions in the ground configuration is assumed. The strongest contributions of metastable parent ions arise from the 5p55d2 and 4 f135d2 configurations.
... where Eq. (1) represents the analytical form of the universal shape function for electron-impact ionization of H-like ions of Aichele et al. 33 Figure 5 shows the Cl 2+ branching ratio as a function of the photon energy. Similar to Fig. 1, a set of Voigt functions representing the various below threshold resonances were added to a constant background due to Cl 2p, Cl 2s, and C 1s contributions. ...
The fragmentation of the tetrachloromethane molecule following core-shell photoexcitation and photoionization in the neighborhood of the chlorine K-edge has been studied by using time-of-flight mass spectroscopy and monochromatic synchrotron radiation. Branching ratios for ionic dissociation were derived for all the detected ions, which are informative of the decay dynamics and photofragmentation patterns of the core-excited species. In addition, the absorption yield has been measured with a new assignment of the spectral features. The structure that appears above the Cl 1s ionization potential in the photoionizationspectrum has been ascribed to the existing connection with electron-CCl4scattering through experimental data and calculations for low-energy electron-molecule cross sections. In addition, the production of the doubly ionized Cl fragment, Cl²⁺, as a function of the photon energy has been analysed in the terms of a simple and an appealing physical picture, the half-collision model.
... For the knockout probability P KO (E), the analytical form of the universal shape function for electron impact ionization of H-like ions of Aichele et al. [63] was adopted. Since the knockout in DPI describes a half collision between the ejected photoelectron and the residual ion, the choice of the shape function was based on the similarity of electron impact ionization of a H-like ion to the KO part of the double photoionization of the corresponding He-like ion [20,[58][59][60]. ...
Single-photon double K-shell ionization of low-Z neutral atoms in the range 12≤Z≤23 is investigated. The experimental method was based on measurements of the high-resolution K{alpha}{sup h} hypersatellite x-ray spectra following the radiative decay of the K-shell double-vacancy states excited by monochromatic synchrotron radiation. The photon energy dependence of the double K-shell ionization was measured over a wide range of photon energies from threshold up to and beyond the maximum of the double-to-single photoionization cross section ratios. From the high-resolution x-ray emission spectra the energies and linewidths of the hypersatellite transitions, as well as the K{alpha}{sub 1}{sup h}:K{alpha}{sub 2}{sup h} intensity ratios, were determined. The relative importance of the initial-state and final-state electron-electron interactions to the K-shell double photoionization is addressed. Physical mechanisms and scaling laws of the K-shell double photoionization are examined. A semiempirical universal scaling of the double-photoionization cross sections with the effective nuclear charge for neutral atoms in the range 2≤Z≤47 is established.
... σ As mentioned earlier, to extract the parameters nl and η nl of GKLV, the model was applied to some selected ionic targets, namely C 5+ and Ne 8+ in the K-shell; N 3+ , Ne 3+ and U 82+,89+ in the L-shell; and Si 3+ , S 4+ , Ar 5+ , Cr 8+ , Ti 2+ and Ni 5+ in the M-shell. The data are taken from [34,35] for C 5+ ; [34,36] for Ne 8+ ; [34,37,38] for N 3+ ; [39,40,41,42] for U 89+ ; [34,43] for Ne 3+ ; [41,42,44] for U 82+ ; [45] for Si 3+ ; [46] for S 4+ ; [47] for Ar 5+ ; [48] for Cr 8+ ; [49] for Ti 2+ ; and [50] for Ni 5+ . ...
... The sources of the experimental EIICS data are Falk and Dunn [52] for Be + ; Donets and Ovsyannikov [34] for C +,2+ , N +,2+,4+ , O +,3+,4+ and Ne 4+,5+,6+,7+ ; Crandall et al [53,54] for N 4+ and O 3+,4+ ; Duponchelle et al [36] for Ne 6+,7+ ; Defrance et al [55] for Ne 7+ ; Aichele et al [35] for Ne 7+ ; ...
The recently proposed generalized Kolbenstvedt model (GKLV) of Haque et al (2007 Eur. Phys. J. D 42 203), for the electron impact ionization (EII) of atoms, was applied to a wide range of K-, L- and M-shell electrons of ionic targets from threshold to 1 MeV incident energy. The set of species-independent parameters, two for each of the ionized orbits, is the same as that for neutral targets, and provides an excellent account of the EII cross-sectional data for 36 ions, including those belonging to Li, Be, B, C, N, O and Ne electronic sequences as well as those having 3s-, 3p- and 3d-configurations of the M-shell in a consistent manner. The performance of GKLV is found to be better than that of the modified version of the BELL model (Haque et al 2006 Phys. Rev. A 73 052703, Haque et al 2006 Phys. Scr.
74 377).
... As we have seen before, the double-to-total photoionization ratio of an atom A is approximately proportional to the electron-impact cross section for the corresponding ion A + [see Equation (5)] (Samson, 1990). In addition, there is a simple electron-impact scaling law for the hydrogen isoelectronic sequence (Aichele et al., 1998): ...
... De même l'agrégat après ionisation modifie les niveaux énergétiques (U) de l'ion pour devenir (U * ). Les énergies (I * , U * ) sont données par les équations (4,5), dans le cas de la première capture électronique. Si on prend comme niveaux énergétiques de l'ion ceux d'un ion hydrogénoide de nombre atomique (q) (eq.9), alors on peut retrouver à partir de l'équation (8) sur quel niveau excité (n) se fera la capture (eq.10) et ce en fonction de la charge (q) et de l'énergie d'ionisation de l'électron capturé (I). ...
... De même l'agrégat après ionisation modifie les niveaux énergétiques (U) de l'ion pour devenir (U * ). Les énergies (I * , U * ) sont données par les équations (4,5), dans le cas de la première capture électronique. Si on prend comme niveaux énergétiques de l'ion ceux d'un ion hydrogénoide de nombre atomique (q) (eq.9), alors on peut retrouver à partir de l'équation (8) sur quel niveau excité (n) se fera la capture (eq.10) et ce en fonction de la charge (q) et de l'énergie d'ionisation de l'électron capturé (I). ...
The first part of the thesis is devoted to SIMPA ECR ion source caracterization, first, I explored the ion source's capacities on the point of view of extracted currents for three elements, argon, krypton and neon. By analyzing the Bremsstrahlung spectra, I determined the electronic temperature in the plasma and the electronic and ionic densities. In a second time, I recorded high resolution X-spectra of argon and krypton plasma's. By taking into account the principal mechanisms of production of a K hole in the ions inside the plasma, I determined the ionic densities of the high charge states of argon. Lastly, I highlighted a correlation between the ions charge states densities with the intensities of extracted currents.
The second part of the thesis is devoted to Ne9+- argon clusters collisions. First, I presented simple and effective theoretical models allowing to interpret the phenomena occurring during a collision, on the point of view of the projectile. I carried out a simulation for a collision of an ion Ne9+ with an argon cluster of a given size, this to know the energy levels populated during the electronic capture and to follow the number of electrons in each projectile shell. Lastly, I presented the first results of a collision between a Ne9+ beam and argon clusters. These results, have enabled me by using projectile X-ray spectroscopy during the ions-clusters collision, to evidence a strong clustering of targets atoms and to highlight an electronic multicapture in the projectile ion excited states.
The correct understanding of the behavior of highly stripped ions immersed in a dense plasma environment is a hitherto challenge for theory and it is of importance in various applications. Here, we developed four kinds of novel theoretical models to the determination of the spectral properties and collision dynamics of H-like ions in dense and hot plasmas by employing the analytical potential to describe the interactions among the charged particles: (i) The EPPP model within the relativistic scheme; (ii) The multiconfiguration Dirac-Fock model within the framework of relativistic self-consistent iteration approximation; (iii) The generalized pseudospectral method within the relativistic framework; and (iv) An analytic formula based on the Hartree-Fock method and the irreducible tensor theory within the non-relativistic regime, derived from a solution of Schrödinger equation. As a typical example, energy eigen-values, radiative transition properties, spectral line shifts, and electron impact excita-tion and ionization cross sections of the selected N 6+ and Ne 9+ ions are determined for several temperature-density cases, characteristic of inertial confinement fusion plasmas. A comparison of these results with each other and the results from earlier calculations as well as with the available experimental data is provided. The present study not only extends our understanding of the dense plasma shielding
effects, but also opens the way for future investigations allowing accurate predictions of spectral properties of ions in dense and hot plasmas aimed at providing precision data for various practical applications.
