Total Cross Sections For Single-electron Capture Research Articles

Single-electron capture in ion-ion collisions

The prior versions of the three-body boundary-corrected first Born approximation (CB1-3B) and the three-body boundary-corrected continuum intermediate states method (BCIS-3B) are applied to calculate the state-selective and state-summed total cross sections for single-electron capture from hydrogen-like ion targets (He+, Li2+) by fast completely stripped projectiles (H+, He2+, Li3+). All calculations are carried out for single-electron capture into arbitrary n l m final states of the projectiles, up to n = 4. The contributions from higher n shells are included using the Oppenheimer n?3 scaling law. The present results are found to be in satisfactory agreement with the available experimental data.

Differential and total cross sections for charge transfer and transfer-excitation in ion-helium collisions

Total cross sections for single charge transfer in collisions of multicharged bare ions with ground-state helium atoms at incident energy ranging from 40 to 5000 keV/amu have been calculated in the framework of a four-body model of final channel distorted-wave (FC-DW-4B) approximation. In this formalism, distortion in the final channel related to the Coulomb continuum of the target and the Coulomb interaction between the passive electron in the target with the projectile are included. In all cases, total single electron-capture cross sections have been calculated by summing over all contributions up to $n=3$ shells and subshells. It has been observed that the contribution of the capture cross sections into excited states have insignificant contributions for symmetric collisions. Comprehensive comparisons are made between the four body model of boundary corrected continuum intermediate-state approximations [Phys. Rev. A 83, 032706 (2011)] and the present FC-DW-4B model. The main purpose of the present study is to investigate the relative importance of dynamic electron correlation and the role of passive electron in the target at intermediate and high impact energies. In addition, projectile angular differential cross sections (DCS) for charge transfer and transfer-excitation in $p\text{-He}$ collisions are calculated at different impact energies. At low projectile energies, the present DCS data exhibits the typical steeply decreasing dependence on the projectile scattering angles, whereas at high impact energies, the double-scattering region centered on the Thomas angle is obtained. Detailed comparisons with the available experimental data and other theories are reported with the purpose of further assessing the relevance of the present model at different impact energies. Overall, the calculated cross sections show good agreement with the available experimental findings.

Four-body charge transfer processes in collisions of bare projectile ions with helium atoms

Single-electron capture by a bare ion from a helium atom at intermediate and high energies in the framework of four-body distorted wave (DW-4B) approximation in both prior and post form has been considered. In the entrance channel, the initial bound state wave function is distorted by the incoming projectile ion, and the corresponding distortion is related to the Coulomb continuum states of the active electron and the residual target ion in the field of the projectile ion respectively. Continuum states of the active electron and the projectile ion in the field of the residual target ion are also included in the exit channel. It may be mentioned that the effect of dynamic electron correlation is explicitly taken into account through the complete perturbation potential. The total single-electron capture cross sections are obtained by summing over all contributions up to n = 3 shells and sub-shells respectively. In addition, the differential cross sections for alpha particle–helium collision are calculated at impact energies of 60, 150, 300, 450, and 630 keV amu−1, respectively. The cross sections exhibit a monotonically decreasing angular dependence, with clear peak structures around 0.1 to 0.2 mrad being found at low impact energies. The current theoretical results, both in prior and post forms of the transition amplitude for symmetric and asymmetric collision, are compared with the available theoretical and experimental results. Current computed results have been found to be satisfactory in comparison with other theoretical and experimental findings.

Single-electron capture collisions of ground and metastable Ne2+ ions with molecular gases

Using the translational energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture in collisions of Ne2+ with N2, CO2 and H2O at laboratory impact energies between 50 and 400 eV and 0° scattering angles. In all the collision systems studied here, reaction channels have been observed which indicate the presence of the long-lived metastable states of (2s2 2p4 1D and 1S) in the Ne2+ incident beam. These measurements also indicate that capture from the metastable states into excited states of the projectile product ions is the most important inelastic process. Contributions from capture accompanied by the excitation and ionization of the target product are also detected. In addition, the energy dependence of the total single-electron capture cross sections is studied and found to slowly increase with increasing impact energy. The present data are compared with the theoretical calculations of the classical over the barrier, extended classical over the barrier and Landau–Zener models.

Mutual neutralization in H+ − H− collisions by electron capture

State-selective and total cross-sections for single-electron capture from H− by H+ covering the incident energy range from 10 to 3000 keV are computed by means of the four-body boundary corrected first Born (CB1-4B) approximation. A crucial connection between the Coulomb-distorted asymptotic state in the entrance channel and the pertinent perturbation, which causes the transition in the H+ − H− collisions, is consistently used in our computations of the “prior” version of cross-sections. The obtained results from the CB1-4B method clearly outperform the earlier findings by the close-coupling methods for the same problem. Comparisons with the available measurements are carried out and excellent agreement with the CB1 method is recorded down to impact energies as low as 10 keV.

Single-electron capture from helium by fast protons

Single-electron capture in p–He collisions has been calculated at incident projectile energies ranging from 20 to 11 000 keV by means of the four-body boundary corrected continuum intermediate state approximation. The effect of dynamic electron correlations is explicitly taken into account through the complete perturbation potentials. Total single-electron capture cross-sections have been calculated by summing over the contributions up to n=2 shells and sub-shells. The differential cross-sections are calculated at impact energies in the range from 30 to 300 keV. Overall, the calculated cross-sections are in good agreement with recent experimental findings.

Single-electron capture processes in slow collisions ofHe2+ions withO2,NH3,N2, andCO2

Using the translational energy-gain spectroscopy technique, we have measured the energy-gain spectra and absolute total cross sections for single-electron capture (SEC) in collisions of ${\mathrm{He}}^{2+}$ ions with ${\mathrm{O}}_{2}$, $\mathrm{N}{\mathrm{H}}_{3}$, ${\mathrm{N}}_{2}$, and $\mathrm{C}{\mathrm{O}}_{2}$ at laboratory impact energies between 25 and $400\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{amu}$. The measured spectra for the ${\mathrm{He}}^{2+}\ensuremath{-}{\mathrm{N}}_{2}$ and $\mathrm{C}{\mathrm{O}}_{2}$ collision systems show that the dominant reaction channel is due to dissociative transfer ionization (i.e., SEC accompanied by ionization of the molecular target ion). In the case of the ${\mathrm{He}}^{2+}\ensuremath{-}\mathrm{N}{\mathrm{H}}_{3}$ collision system, nondissociative single-electron capture into $n=2$ states of ${\mathrm{He}}^{+}$ with production of $\mathrm{N}\mathrm{H}_{3}{}^{+}$ in the ground state is predominantly populated. These processes are observed to be the dominant reaction channels over the entire impact energy region studied and at laboratory scattering angles between 0\ifmmode^\circ\else\textdegree\fi{} and 8\ifmmode^\circ\else\textdegree\fi{}. The energy dependence of total cross sections for SEC are also measured and found to slowly increase with increasing impact energies. The measured cross sections are also compared with the available measurements and theoretical results based on the Demkov and Landau-Zener models.

Total-capture cross sections for very slow Ar4+-Ar and Ar6+-Ar collisions.

We present experimental and calculated total single-electron capture cross sections for Ar{sup 4+}-Ar collisions in the laboratory energy ranges 100--800 and 10--800 eV, respectively. The experimental results for post-collisional energy and angular distributions of Ar{sup 3+} extend down to 19 eV; below 100 eV a part of the angular distribution falls outside the {plus minus}9{degree} angular acceptance. The absolute calibration of our Ar{sup 4+}-Ar results is achieved by means of normalization of relative Ar{sup 6+}-Ar single-capture cross sections to absolute total cross sections from the literature. Calculated single-electron capture cross sections for Ar{sup 4+}-Ar are obtained from a multichannel Landau-Zener model with semiempirical coupling strengths that reproduce the experimental state-selective angular distributions. When these theoretical angular distributions are integrated over the experimental angular acceptance, the agreement between experimental and calculated cross sections is excellent down to 19 eV. We also present total experimental cross sections for removing two electrons from Ar for collisions with Ar{sup 6+} at 800, 600, and 450 eV, and for 800-eV collisions with Ar{sup 4+}.

Electron transfer and projectile excitation in single collisions

Studies of electron transfer (capture) and projectile excitation occuring together in a single encounter are reviewed. This combined capture and excitation can result from either a correlated or an uncorrelated interaction. The correlated process is referred to as resonant transfer and excitation (RTE), while the uncorrelated process is called nonresonant transfer and excitation (NTE). RTE is analogous to dielectronic recombination (DR) which occurs in the interaction between an ion and a free electron. Experimental and theoretical works leading to establishing the existence of RTE are reviewed as well as considerations relevant to distinguishing RTE from NTE. The dependences of RTE on projectile atomic number (14≤ Z≤23) for Li-like ions, and on projectile charge state for H-like to Ne-like ions have been measured and compared with theory. The effect of the target electron momentum distribution on RTE has been demonstrated by comparing measurements for H 2 and He targets. Measurements of RTE involving L-shell excitation have been conducted and compared with K-shell results. All of the measured RTE cross sections to date for H 2 and He targets are in reasonable agreement with calculations based on theoretical DR cross sections averaged over the target electron momentum distribution; however, systematic discrepancies between experiment and theory exist. Additionally, it has been found that RTE can contribute considerably to total single-electron capture cross sections in the region where RTE is important, accounting for nearly half of the total capture events for calcium ions colliding with H 2.