Cross Sections For Single Electron Capture Research Articles

N + charge transfer in N 2 at low-keV collisions

The absolute differential and total cross-sections for single electron capture at energies between 0.5 and 5.0 keV are reported. The reduced differential cross-sections shows an overall increase of at least one order of magnitude and a monotonic decreasing behavior at all the collision energies studied in this work. The total cross-sections for single electron capture are compared with previous experimental measurements. The total cross-section results presented in this paper and obtained by integration of the measured differential cross-sections agree with previous measurements using a beam of pure ground state ions.

State-selective Charge Transfer Studies Relevant to Solar Wind–Comet Interactions

We report relative experimental and absolute theoretical n-state-selective, nondissociative, single-electron capture cross sections for a number of collision systems typical of the solar wind-comet interactions. The experimental measurements were carried out using the technique of cold-target recoil-ion momentum spectroscopy and involved the N7+ and O7+ projectile ions and, for the first time, the H2O, CO2, and CO molecular targets, as well as the He atomic target. The theoretical calculations were performed using the classical trajectory Monte Carlo (CTMC), the Landau-Zener (LZ), and the classical over-the-barrier (COB) models. The models, with CTMC favored, agree reasonably well with the measurements and can be used in the near term to aid in the modeling of cometary X-ray and EUV emission. The pathways through which multiple-electron capture processes contribute to the cometary X-ray and EUV emission are also discussed.

Electron capture in collisions between negative and positive ions

Collisions between negative and positive atomic ions are investigated. The ionic wave function is expressed in terms of the Coulomb Green’s function. Normalizing this function allows the system of two ions to be described completely. The exchange matrix elements turn out to be the sums of products of the Coulomb wave functions over degenerate states. These sums are expressed in terms of the quadratic form of the wave function for a state with zero angular quantum numbers, l=m=0. The nonadiabatic coupling of quasi-crossing terms with other terms of the system is analyzed; this effect significantly increases the cross section for single-electron capture.

Single- and double-electron capture inlow-energy Ne10+-He collisions

We present a combined experimental/theoretical study ofNe10+-He collisions in the 50⩽E⩽150 keV impact energy range using improved-resolution recoil ion momentumspectroscopy. Total and differential cross sections for single-electron capture onto the levels n = 3,4,5 and 6 ofNe9+(nl) and double-electron capture onto series ofdoubly excited states 3, n and 4, n with n = 4, 5 and 6 of Ne8+ have been obtained. They are found to be in goodagreement with close-coupling calculations. Populationmechanisms for the dominantly populated double-capture channelshave been deduced from this work. Special emphasis isbrought to the analysis of the partial stabilization ratios toobtain a new insight into the velocity dependence of total stabilization ratios.

Experimental investigation of the formation of N atoms in N+[sbnd]Ne, Kr, and Xe collisions

Total cross sections for single electron capture by N+ ions impinging on Ne, Kr, and Xe were measured in the energy range of 1.0–5.0 keV. The electron capture cross sections for all the targets studied are found to be in excellent agreement with previous data in the low-energy range. These results give a general shape of the whole curve of single electron capture cross sections for the N+Ne system over a wide range of energy. For the cases of N+Kr and N+Xe systems, semiempirical calculation using the two-state approximation are in very good agreement with present cross-section data.

Single-electron capture and transfer ionization in collisions ofLi3+ions with helium

The total cross sections for single-electron capture and transfer ionization are computed for ${\mathrm{Li}}^{3+}+\mathrm{H}\mathrm{e}$ collisions in a four-body distorted-wave formalism. The contribution from the $e\ensuremath{-}e$ interaction during the collision is evaluated. Comparison between the present theoretical results and measurements at 50--5000 keV/amu yields satisfactory agreement. The continuum distorted-wave four-body method employed can provide information about the relative significance of the dynamic interelectron interaction in the collisions under study.

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 $(0.76\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}.$

Low-energy electron capture byCl7+from D using merged beams

Measurements of the absolute total cross section for single-electron capture in collisions of ${\mathrm{Cl}}^{7+}$ with ground-state atomic deuterium are reported in the energy range 4.6--428 eV/amu. These measurements represent the highest charge state yet reported using the Oak Ridge National Laboratory ion-atom merged-beams apparatus. The electron-capture cross section for ${\mathrm{Cl}}^{7+}$ is observed to decrease at lower energies, in contradiction to what is expected from a popular simple model and speculation from previous measurements for highly charged $(7+)$ ions with multielectron cores. The observed low-energy behavior is interpreted using coupled-channel molecular-orbital hidden-crossing calculations for ${\mathrm{N}}^{7+}+\mathrm{D}.$

Charge transfer inH++Arcollisions from 10 to 150 keV

Total as well as partial cross sections for single-electron capture of ${\mathrm{H}}^{+}$ on Ar are calculated by the semiclassical impact parameter method, using a two-center atomic basis expansion, in the impact energy range 10--150 keV. The resulting total cross sections are in good agreement with previous experimental data. Partial cross sections agree qualitatively with measurements at high energies, while at low energies the experimental data are found to be approximately six times smaller than the present results.

Absolute electron capture cross sections of Kr + with Ne atoms

The absolute differential and total cross sections for single electron capture at energies between 1 and 5 keV are reported. The reduced differential cross sections scale reasonably well, showing an overall increase of two orders of magnitude and three maxima at different collision energies. We deduce, from the experimental differential cross section, that the electron capture channel “opens” at a critical projectile-target separation between 2.88 a 0 and 3.15 a 0 and that at least two different processes are involved in the present energy range. The single electron capture cross section of Kr + ions in various media is shown. It has been found that the dependence of the single electron capture cross section with the nuclear charge of the target atoms is oscillatory. Keywords: Electron transfer; Angular distributions; Absolute cross sections; Kr +; Kr 0

Single Electron Capture in Slow H- + A3+ Collisions

The cross section of single-electron capture in slow H- + A3+ → H + A2+(n) collisions is calculated in the one-electron approximation by using the close coupling approach. It is found that the change of the electronic configuration, that takes place at every avoided crossing of the ionic and covalent energy terms, is a source of nonadiabatic transitions in the system. This effect leads to a substantial increase of the total cross section and produces an effective repopulation of individual covalent states.

State-selective electron capture in (0.5–50)-keV/uC5+−Hecollisions studied by cold-target recoil-ion momentum spectroscopy

Cross sections, differential in translational energy gain and projectile scattering angle, for single- and double-electron capture processes in collisions of ${\mathrm{C}}^{5+}$ ions with He at laboratory energies between 0.5 and 50 keV/u, have been studied experimentally by means of a high-resolution cold-target recoil-ion momentum spectroscopy. The translational energy spectra for single-electron capture show that capture into the ${\mathrm{C}}^{4+}$ $(n=3)$ state is the dominant reaction channel observed over the entire collision energy region studied, in agreement with close-coupling calculations. However, capture into $n=2$ and $n>~4$ states is only significant at $E>~4 \mathrm{k}\mathrm{e}\mathrm{V}/\mathrm{u}.$ Transfer excitation processes contribute only very weakly to the total cross sections for single-electron capture (2--4 %). This contribution is considerably smaller than the close-coupling prediction. The autoionizing double-electron-capture (transfer ionization) spectrum clearly shows that ${\mathrm{C}}^{3+}$ ${(2l,2l}^{\ensuremath{'}})$ states are populated at the lowest impact energy, whereas contributions from capture into ${\mathrm{C}}^{3+}$ ${(2l,n}^{\ensuremath{'}}{l}^{\ensuremath{'}})$ states with ${n}^{\ensuremath{'}}>~3$ increase as the impact energy is increased and become the dominant process at $E=35 \mathrm{k}\mathrm{e}\mathrm{V}/\mathrm{u}.$ State-selective and differential cross sections have also been measured and compared with the close-coupling and multichannel Landau-Zener calculations.

State selective capture cross sections in slow collisions of fully and partially stripped ions with the molecular hydrogen: a progress report

Single-electron capture cross sections from H 2 by a number of fully and partially stripped ions (2≤ q≤6) has been calculated using a semi-classical Molecular Orbital approximation. During the course of the collision a transient quasi-molecule comprising the entrance and various exit channels of the charge-transfer reactions is considered. Freezing the molecular details of the target, the effective binding of the active electron inside the transient molecule is simulated employing pseudo-potential. A multi-channel calculation is carried out in which the number of molecular states to be coupled together is decided by the collision dynamics of the individual pair. The calculated cross sections agree very well with the available experimental results. Although the Landau–Zener mechanism is mainly responsible for the observed state-selective charge-exchange process, no generalization in terms of projectile charge or structure is possible to predict the behavior of individual interactions. The total cross sections, along with their ℓ-distribution, for the O 6+–H 2 system are reported here for the first time.

State‐selective single‐electron capture in very slow collisions of Arq (q = 4–8) ions with neon

State-selective differential cross sections for single-electron capture processes in very slow collisions of Ar q+ (q = 4–6) ions with neon (Ne) have been studied experimentally at laboratory impact energies between 0.4 and 4 qeV/amu and scattering angles between 0 ° and 8 ° by means of the translational energy-gain spectroscopy technique. The translational energy spectra show that the dominant reaction channels are due to capture into excited states of the projectile product Ar(q−1)+. However, at very low energies, other channels due to transfer excitation processes are found to open at large scattering angles. The energy-gain spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model and the extended version of the classical over-the-barrier model. The energy dependence of cross sections for single-electron capture by Ar q+ (q = 4–8) ions from Ne are also measured and found to be nearly constant with changing impact energy, but increase with an increase in the projectile charge state. The data are also compared with available measurements and theoretical calculations. Copyright © 1999 John Wiley & Sons, Ltd.

State-selective single-electron capture in very slow collisions of Arq+ (q = 4-8) ions with neon

State-selective differential cross sections for single-electron capture processes in very slow collisions of Arq+ (q = 4–6) ions with neon (Ne) have been studied experimentally at laboratory impact energies between 0.4 and 4 qeV/amu and scattering angles between 0 ° and 8 ° by means of the translational energy-gain spectroscopy technique. The translational energy spectra show that the dominant reaction channels are due to capture into excited states of the projectile product Ar(q−1)+. However, at very low energies, other channels due to transfer excitation processes are found to open at large scattering angles. The energy-gain spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model and the extended version of the classical over-the-barrier model. The energy dependence of cross sections for single-electron capture by Arq+ (q = 4–8) ions from Ne are also measured and found to be nearly constant with changing impact energy, but increase with an increase in the projectile charge state. The data are also compared with available measurements and theoretical calculations. Copyright © 1999 John Wiley & Sons, Ltd.

Absolute differential and total cross sections for single electron capture in low-energyKr+−Arcollisions

Absolute differential and total cross sections for single electron capture were determined from ${\mathrm{Kr}}^{+}$ ions on Ar in the energy range 0.3--5.0 keV. Using reduced variables $[\ensuremath{\tau}=E\ensuremath{\theta}$ vs $\ensuremath{\theta}\mathrm{sin}(\ensuremath{\theta})d\ensuremath{\sigma}/d\ensuremath{\Omega}=\ensuremath{\rho}],$ we deduced, from the experimental differential cross sections, that the electron capture channel ``opens'' at a critical projectile-target separation between ${1.63a}_{0}$ and ${2.21a}_{0}$ in the present energy range and that at least two different processes are involved. The total cross section for single electron capture is compared with other available measurements. These results give a general shape of the curve for single electron capture cross sections for the ${\mathrm{Kr}}^{+}\ensuremath{-}\mathrm{A}\mathrm{r}$ system in a wide range of energy.

Longitudinal and Transverse Recoil Electron Capture Processes in 0.5–50 keV/u C5+–He Collisions

A high resolution cold target recoil-ion momentum spectroscopy (COLTRIMS), capable of measuring simultaneously the longitudinal and the transverse recoil momenta, has been used for the study of state-selective single- and double-electron capture by C5+ ions from He at laboratory impact energies between 0.5 and 50 keV/u. The longitudinal momentum spectra for single-electron capture indicate that the dominant reaction channel observed is due to capture into the n = 3 state of the product C4+ ions. This reaction channel contributes mainly to the total cross section for single-electron capture, in agreement with the close-coupling calculations. At a collision energy of 35 keV/u, the spectrum for the autoionizing double-electron capture illustrates that capture into the asymmetrical C3+(2l, n'l') states (n' = 3 to ∞) dominates, while capture into the symmetrical C3+(2l, 2l') and C3+(3l, 3l') states show less contributions. True double-electron capture occurs predominantly into the asymmetrical C3+(2l, n'l') states with n' = 3 to ∞.

Production of and in collision of ions with Kr

Absolute differential and total cross sections for single-electron loss and capture were measured from ions on Kr in the energy range of 1.0-5.0 keV. The reduced differential cross sections as a function of are shown to scale reasonably well for both products studied. For single-electron loss, our cross sections are found to be of the order of magnitude of , while for single-electron capture the magnitude is . The measured total cross sections are compared with theoretical models available in the literature.

Low-energy single-electron capture cross sections in C6+/C4+-Na(3s) and N7+/N5+-Na(3s) collisions: Molecular state approach

The low-energy state-selective capture cross sections for single-electron transfer from the ground state of Na(3s) atoms by fully (C6+ and N7+) and partially stripped (C4+ and N5+) ions have been calculated using the semiclassical approximation in the molecular orbital formulation augmented with the proper electron translation factor. The method of pseudopotential is invoked to account for the interaction of the active electron with the moving nuclei, whose relative motion is considered via a straight-line trajectory. Although both C4+ and N5+ have identical He-like structure, their roles reveal very different collision dynamics. The projectile C4+ exhibits a distinctive role due to its finite core; a low-energy structure in the total capture cross section for C4+–Na(3s) collisions is observed and explained. For bare projectiles (C6+ and N7+) there remains an increasing tendency of the Stark mixing to characterize the electron transfer processes; it enhances the population of the higher 𝓁 states. The 𝓁 distribution of the charge-transfer cross section for various projectile is also discussed. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 75: 385–398, 1999

Single-electron loss and capture for 1.0-5.0 keV colliding with He

Absolute differential and total cross sections for single-electron loss and capture were measured from ions on He in the energy range of 1.0-5.0 keV. The reduced differential cross sections ( versus ) are shown to scale reasonably well for each of the two processes studied. For single-electron loss, our cross sections are found to be of the order of magnitude of . An extrapolation of the high-energy results to low energies shows good agreement with the present data. The total cross section for single-electron capture is compared with other available measurements. These results give a general shape of the whole curve of single-electron capture cross sections for the system over a wide range of energy.