Cross Sections For Double Electron Capture Research Articles

Single- and Double-electron Capture Cross Sections for O6+ Ion in Collisions with H2 Molecules

Single- and double-electron capture (SEC and DEC) processes occurring in O6+ and H2 collisions are investigated in a wide-energy domain ranging from 0.1 to 100 keV u−1. Total and partial cross sections are calculated using a three-center, two-active-electron, semiclassical nonperturbative approach. To date, our close-coupling description of the collision is the most elaborate one in terms of accounting for electron correlation, molecular structures, and active channels. Our results are, in general, in good agreement with the available experimental ones for both total and partial cross sections. The comparison between the present calculations and available experimental data suggests that about 70% of the autoionization double capture may contribute to the measured SEC cross sections through postcollisional autoionization, while the stabilization of 30% of doubly excited states via the autotransfer to Rydberg states mechanism contributes to the measured DEC ones. Furthermore, we extend the understanding of the electron-capture processes on this system to impact energies above 20 keV u−1 for which no data exists. Our work provides new data for these electronic processes, which will be helpful for modeling astrophysical X-ray emissions induced by charge exchange.

Electron capture and loss of O+ projectile in collision with water near the Bragg Peak Energies

The combined experimental and theoretical works of the study of the absolute single and double electron loss (stripping) and single and double electron capture cross sections for 0.2–1.2 MeV O+ projectiles colliding with water molecule are presented. In order to mimic the experimental observation we performed three, four and five-body classical trajectory Monte Carlo calculations. In our model the O+ projectile is either one, (two or three) particle(s) depending on the model used (3, 4 or 5 body model, respectively) and the water target is taken into account as two virtual particles. We found that the calculated cross sections are in agreement with the present experimental data. Moreover, the similarity of the present data with an isoelectronic system, the methane molecule allows us to draw a common curve through both data sets.

Single and double electron capture cross sections in keV-collisions between fully stripped ions with helium atom

SynopsisWe present cross section calculations for single-, double-capture, and double capture to auto-ionizing states occurring in the course of collisions between fully stripped ions Aq+ (q≤10) and helium atom at impact energies ranging from 0.25 to 625 keV/u. These calculations were performed by applying a semiclassical nonperturbative close coupling approach, based on the expansion of the scattering wave function into asymptotic bielectronic states with proper translational conditions and including both static and dynamic electronic correlation.

Comparative study of single and double electron capture from atoms by fast bare ions

Total cross sections for single and double electron capture in collisions of bare ion with helium-like atoms are calculated at energies ranging from 50 to 6,000 keV/amu. The present calculations are carried out using four-body formalism of Coulomb–Born distorted wave formalism and boundary corrected continuum intermediate state approximation. We have made a comparison between single and double electron capture cross sections using both the methods in wide range of energies at different charge state of the projectile. Total cross sections have been calculated by summing over all the contributions up to n = 2 shells and sub-shells. It is also noted that double electron capture cross sections are small thorough out the energy region compared with the single electron capture cross sections. However, the present computed results for asymmetric collisions have been compared with available theoretical and experimental results. We find that our numerical results for total cross sections show good agreement with the available experimental findings.

Influence of multi-electron charge-changing processes on the average charge states of heavy ions passing through a He-gas target

Average (equilibrium) charge states q¯ of heavy Acq+ (Z=89), Noq+ (Z=102) and Flq+ (Z=114) ions passing through a He-gas target at energies 50–150keV/u are calculated with account for single- and multi-electron loss and capture cross sections. The q¯ values are obtained by solving the balance equations for equilibrium charge-state fractions and using single-, double- and triple-electron loss cross sections and single- and double-electron capture cross sections. Calculations of all electron-loss and single-capture cross sections are performed using available computer codes, and double-electron capture cross sections are estimated using a new semi-empirical formula obtained in this work on the basis of available experimental data for He target atoms. The account for the multi-electron processes changes significantly (up to about 25%) the q¯ values compared with those calculated with only single-electron cross sections and leads to a better agreement with experimental data.

Electron capture and deprotonation processes observed in collisions between Xe8+and multiply protonated cytochrome-C

Electron-transfer processes in interaction between highly charged ions and multiply protonated proteins have been studied. Collisions between Xe${}^{8+}$ at 96 keV and protonated cytochrome-C at selected charge state ($q$ from 15+ to 19+) result in mass spectra composed mainly of intact molecular ions. From the spectra, single and double electron capture processes by Xe${}^{8+}$ from the protonated molecular ions were identified and the relative cross sections were measured. An unexpected process, the deprotonation process, was also observed. It is tentatively attributed to the loss of a proton induced by the strong electric field carried by the projectile ion in long-distance collisions. Upon charge variation of the molecular target from 15 to 19, the single and double electron capture cross sections remain nearly constant, while the relative cross section of the deprotonation process increases dramatically from 0.8% (\ifmmode\pm\else\textpm\fi{}0.1%) to 17% (\ifmmode\pm\else\textpm\fi{}1%). This strong charge dependency is explained by the decrease of the proton affinities with the charge. This proton removal process has not been observed previously. It seems to be specific to the long-distance Coulomb interactions between protons bound along the protein chain and the highly charged atomic ions.

Electron capture cross section in collision of multi-charged neon ions with ground state hydrogen and helium

The classical trajectory Monte Carlo method and the post form of three-body boundary corrected continuum intermediate state (BCCIS-3B) approximation are employed to calculate the cross sections for total and state-selective electron capture in collision of highly charged Neq+ ions with ground state hydrogen atom in the intermediate to high energy region. In both these methods, the active electron interactions with the partially stripped neon ions are described by a model potential containing both a long-range part and a short-range part. We have also calculated the double electron-capture cross sections in collision of fully stripped neon ion with helium atom in the energy range 80–2,000 keV/amu using the post-form of four-body BCCIS approximation (BCCIS-4B). In BCCIS formalism, the intermediate continuum state of the active electrons with the projectile ion has been taken into account as the projectile charge is greater than the target charge. In addition, state-selective charge transfer cross sections are given in tabular and graphical form.

Nonperturbative treatment of multielectron processes in ion-molecule scattering: Application to He2+-H2collisions

We present a nonperturbative theory to describe multielectronic processes occurring in the course of collisions between an ion and a molecule. The approach is based on the expansion of the electronic scattering wave function onto asymptotic mono- or multicenter states with proper translational conditions and includes both static and dynamical electronic correlations. Therefore, it has a wide application range around intermediate impact velocities $v\ensuremath{\approx}{v}_{e}$, where ${v}_{e}$ is the averaged electron velocity in the initial state. As a first application, we report results on single- and double-electron capture processes in He${}^{2+}$-H${}_{2}$ collisions for impact energies ranging from 0.01 to 25 keV/u. Special emphasis on the prediction of cross sections for double-electron capture into doubly excited states of helium is addressed.

Single- and double-electron capture processes in low-energy collisions of N3+with He

Single-electron capture (SEC) and double-electron capture (DEC) processes in collisions of ground state N{sup 3+} (2s{sup 2} {sup 1}S) ions with He are investigated by using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. The ab initio adiabatic potentials, radial and rotational coupling matrices utilized in QMOCC calculations, are obtained from the multireference single- and double-excitation configuration interaction approach. Total and state-selective SEC and DEC cross sections are presented in the low-energy range from 0.1 eV to 15 keV (i.e., 0.007 eV/u -1.07 keV/u) and rate coefficients in the temperature range from 10{sup 4} to 10{sup 7} K. Our results indicate that the SEC dominates the charge-transfer process in the considered energy region of this collision system and the SEC cross sections are nearly constant in the relatively high-collision energy region, while the DEC cross sections are about 2 orders of magnitude smaller. It is found that, for the SEC processes, in the dominant mechanisms, electrons are captured to exoergic channels N{sup 2+} (2s2p{sup 2} {sup 2}D,{sup 2}S), and for the DEC processes, they are captured to N{sup +} (2s{sup 2}2p{sup 2} {sup 1}D,{sup 1}S). Our calculations also reveal that rotational couplings become important at E > 10 eV/u for SEC andmore » E > 200 eV/u for DEC processes.« less

H+ and He2+ impact charge transfer cross sections of magnesium

H+ impact single and He2+ impact single and double electron capture cross sections of magnesium atoms have been calculated in the modified binary encounter approximation (BEA). The accurate expressions of ion impact \(\sigma _{\Delta {E}}\) (cross section for energy transfer \(\Delta E\)) and Hartree-Fock momentum distributions of the target electrons have been used throughout the calculations. On the basis of the present work it is concluded that inner shell captures by H+ and He2+ ions incident on magnesium atoms contribute partly to single electron capture and partly to transfer ionization cross sections. The calculated He2+ impact double electron capture cross sections of magnesium are in reasonably good agreement with the experimental observations. This indicates the success of the present theoretical approach in study of charge transfer cross sections of atoms as indirect mechanisms do not interfere with double electron capture processes in this case.

Double electron capture cross-sections by protons in collisions with He

Double electron capture (DEC) by protons from He was studied in collisions at energies in the keV regime, theoretically and experimentally. Theoretical cross-sections were calculated using the electron nuclear dynamic approach and a binomial distribution method in the energy range 1–100 keV. Experimental cross-sections were measured by means of the grow-rate method in the energy range of 4–10 keV. The cross-sections measured are consistent with those of the previous data at the high energies of the measured interval and show a different trend for the low energy. This behavior is consistent with those of other DEC cross-sections measured by protons from He-like targets. With the two collision models, it is proven that the reference data for this system are consistent only with the assumption of uncorrelated electrons and with independent target-projectile nuclei dynamics.

Double-electron-capture cross sections forLi3+collisions with He at intermediate-to-high velocities

We have measured double-electron capture cross sections for ${\text{Li}}^{3+}$ projectiles and He targets in the 2.0--5.5 MeV energy range (3.4--5.6 a.u. velocity range). Double-electron-capture cross sections for this collision system were measured before, but only at relatively lower energies. There is a good agreement between the three available sets of experimental data for double capture at the lower end of the present data energy interval, i.e., where the ranges from different measurements overlap. The present measurements for other collision channels that include single and double ionization, single capture, and transfer ionization corroborate the reliability of the data normalization adopted in our work. Our experimental data for double capture are compared with the corresponding theories in order to assess the relative performance of the main two strategies, the semiclassical independent particle model, and the full quantum-mechanical four-body theories. We thoroughly discuss possible reasons for the discrepancies among various theoretical predictions from these two frameworks and point out several potential paths for their improvement.

Single- and double-electron capture cross sections for slowHe2+impact onO2,H2, andD2

Single- and double-electron capture cross sections have been measured for ${\mathrm{He}}^{2+}$ impact on ${\mathrm{O}}_{2}$, ${\mathrm{H}}_{2}$, and ${\mathrm{D}}_{2}$ at impact energies smaller than $2\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu}$. The method applied combines the collection of slow product ions and electrons with primary ion-beam attenuation and stopping in a differentially pumped target gas chamber. Comparison with previous experimental and theoretical results is made. For ${\mathrm{He}}^{2+}$ collisions with ${\mathrm{H}}_{2}$ we find that double-electron capture is more important than single-electron capture below $0.2\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu}$. This result is also confirmed by cross-section measurements for ${\mathrm{He}}^{2+}$ on ${\mathrm{D}}_{2}$.

Double-charge-transfer cross sections in inelastic collisions of bare ions with helium atoms

Double-charge-transfer cross sections into singly and doubly excited states for collisions of $\ensuremath{\alpha}$ particles with helium atoms have been studied in the energy range of 50 to $500\phantom{\rule{0.3em}{0ex}}\mathrm{keV}∕\mathrm{amu}$. We have also studied the double electron capture cross sections into ground states for collisions of $^{7}\mathrm{Li}^{3+}$ and $^{10}\mathrm{B}^{5+}$ with helium atoms. In our study we have applied the four-body boundary corrected continuum intermediate state approximation. The intermediate continuum states of each electron and static correlations of the electrons have been taken into account in this formalism. Present calculated results for total charge transfer cross sections for the reaction $\ensuremath{\alpha}+\mathrm{He}$ and ${\mathrm{Li}}^{3+}+\mathrm{He}$ compare favorably well with the existing experimental and other theoretical predictions. Due to the nonavailability of any theoretical and experimental finding for the reaction ${\mathrm{B}}^{5+}+\mathrm{He}$, the energy variation of capture cross sections into the ground state of ${\mathrm{B}}^{5+}$ ion has been shown within the same energy range. However, charge transfer cross sections into singly and doubly excited states of He are compared with the available theoretical observations only due to nonavailability of any experimental result. In this case as well, agreement is very encouraging.

Charge-changing cross sections of fastH0,1+andHe0,1+,2+projectiles inC60

Electron capture and loss cross sections have been measured for fast light projectile ions of $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ ${\mathrm{H}}^{0,1+}$ and $0.5--2.0\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ $^{4}\mathrm{He}^{0,1+,2+}$ in collisions with ${\mathrm{C}}_{60}$. The gaseous target of ${\mathrm{C}}_{60}$ was prepared by heating ${\mathrm{C}}_{60}$ powder in a target cell to temperatures of $300--500\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, and outgoing charge fractions were measured as a function of the cell temperature. Absolute cross sections are deduced by using two different vapor-pressure data available in literature. Experimental cross sections are examined in comparison with theoretical values obtained from various conventional formulas proposed for atomic targets. In addition, single- and double-electron capture cross sections are also calculated on the basis of a classical model by taking account of the local electron density of ${\mathrm{C}}_{60}$. From a complete set of our experimental cross sections, equilibrium charge fractions are also deduced and found to be essentially the same as carbon-foil data, indicating no gas-solid difference.

Quantum chemistry calculation of excited three center systems: Theoretical study of He2++H2 collisions

Close-coupling calculations of single (dissociative and nondissociative) and double electron capture cross sections in He2++H2 collisions in the range of impact energies 0.5–25 keV/amu are presented and compared with experimental data. The calculations have been carried out at the Franck–Condon level and employing both ab initio expansions, in terms of three-center electronic functions, and the independent particle model approximation. We discuss the mechanisms of the processes and the validity limits of these treatments.

Absolute total one- and two-electron-transfer cross sections ofO3+andO2+with CO at kilo-electron-volt energies

Absolute total one- and two-electron-transfer cross sections for ${\mathrm{O}}^{q+}$ $(q=3,2)$ with CO were measured at $\ensuremath{\sim}1.5q$ keV energies. The measurement was carried out by a technique that combines a laser ablation ion source and a reflection time-of-flight mass spectrometer. The single- and double-electron capture cross sections for ${\mathrm{O}}^{3+}$ with CO are $(1.26\ifmmode\pm\else\textpm\fi{}0.18)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ and $(0.72\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2},$ respectively. The single-electron capture cross section for ${\mathrm{O}}^{2+}$ with CO is $(0.76\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}.$

Scaling laws for single and double electron capture inAq++Hecollisions(q>~ZA−2)at low impact velocities

We present empirical scaling laws, as a function of the projectile charge state, for single and double electron capture in slow collisions between highly charged ions and He atoms at impact velocities of 0.1 and 0.5 a.u. The fitting parameters are shown to be suitable for predicting the populated states in single and double electron capture. The scaling law for single capture is found to be nearly independent of the projectile velocity in the range 0.1--0.5 a.u. The same fitting procedure is followed for double electron capture at the velocity of 0.5 a.u. since independent monoelectronic transitions, due to electron-nucleus interactions, are dominant. At this velocity, the scaling law for the projectile charge dependence of double electron capture cross sections is found to be similar to that for single electron capture. At the lower velocity of 0.1 a.u., where dielectronic processes caused by the electron-electron interaction gain importance, the charge dependence of double capture cross sections is strongly modified.

Energy dependence of cross sections for double-electron capture in 48-132-keV C6++He collisions.

We report on the projectile energy dependence of the cross sections for producing the configurations 2${\mathit{lnl}}^{\ensuremath{'}}$ (n\ensuremath{\ge}3) by double-electron capture in ${\mathrm{C}}^{6+}$+He collisions. The present measurements and calculations, which extend previous work performed on the 90-keV ${\mathrm{C}}^{6+}$+He system, give evidence for dynamic electron-correlation effects in double-capture mechanisms. A significant dependence on the collision energy is found for the cross sections associated with the configurations 2${\mathit{lnl}}^{\ensuremath{'}}$ (n\ensuremath{\ge}5). Moreover, anisotropies of the angular distributions of Auger electrons originating from the configurations 2l3${\mathit{l}}^{\ensuremath{'}}$ are observed at 48 and 132 keV. The capture cross sections for producing some of the terms 2l3${\mathit{l}}^{\ensuremath{'}}$ $^{1}$L are shown to depend on the collision energy. The cross sections for production of the magnetic substates ${\mathit{M}}_{\mathit{L}}$=0 associated with the configurations 2l3${\mathit{l}}^{\ensuremath{'}}$ are found to be the same for both energies of 48 and 132 keV. \textcopyright{} 1996 The American Physical Society.

Partial cross sections for single- and double-electron capture by multiply charged ions colliding with He

Partial cross sections for single- and double-electron capture by multiply charged ions ([ital q]=4 and 5) in low- and intermediate-energy collisions with He were calculated within the two-electron two-center atomic-orbital coupled-channel method. Special care was exerted to account for electron-correlation effects in the reaction process. Absolute single-capture cross sections compare reasonably well with available experiments. The relative behavior of partial cross sections for double-electron capture as well as the relative population of magnetic substates are in good agreement with experiments for B[sup 4+](1[ital s]) and C[sup 5+](1[ital s]) impact.