State-selective Single-electron Capture Research Articles

Study of state-selective single-electron capture in slow Ne7+ colliding with He and H2 target

Using the cold target recoil-ion momentum spectroscopy, we measured the state-selective single electron capture in collisions of 3.5–6.3 keV u−1 Ne7+ ions and He and H2. The Q-value spectra and angular distributions as a function of the projectile incident energy were obtained. The results show that the single electron capture into n = 4 states is the dominant reaction channel for the Ne7+-He system, while the capture into n = 4 and n = 5 states both are dominant processes for the Ne7+-H2 system. The molecular coulombic barrier model and the potential energy curves can qualitatively explain the measured state populations for both systems.

State-selective charge exchange cross sections in collisions of highly-charged sulfur ions with helium and molecular hydrogen

The state-selective cross section data are useful for understanding and modeling the x-ray emission in celestial observations. In the present work, using the cold target recoil ion momentum spectroscopy, for the first time we investigated the state-selective single electron capture processes for S q+–He and H2 (q = 11–15) collision systems at an impact energy of q × 20 keV and obtained the relative state-selective cross sections. The results indicate that only a few principal quantum states of the projectile energy level are populated in a single electron capture process. In particular, the increase of the projectile charge state leads to the population of the states with higher principal quantum numbers. It is also shown that the experimental averaged n-shell populations are reproduced well by the over-barrier model. The database is openly available in Science Data Bank at 10.57760/sciencedb.j00113.00091.

State-selective single-electron capture in intermediate-energy C4+ + He collisions

A combined experimental and theoretical study on single capture in 15--$50\phantom{\rule{0.28em}{0ex}}\mathrm{keV}/\mathrm{u}\phantom{\rule{0.16em}{0ex}}{\mathrm{C}}^{4+} +$ He collisions was performed. State-selective single-electron capture cross sections and projectile scattering angle distributions were obtained by using a reaction microscope. A comparison of the state-selective cross sections with theoretical calculations based on the two-active-electron semiclassical atomic-orbital close-coupling method showed an excellent agreement for the considered impact energies. For the angular differential cross sections, an overall agreement was also obtained between the present experimental and theoretical results. Simulations performed using an extended Fraunhofer-type diffraction model suggest that the undulatory structures observed at small scattering angles for capture to ${\mathrm{C}}^{3+}(1{s}^{2}2s$) and ${\mathrm{C}}^{3+}(1{s}^{2}2{p}_{0}$) can be interpreted as the diffraction pattern of the incident projectile de Broglie wave confined by an aperture defined as the region around the target where the considered capture process is likely. The strong competition between single-electron capture to ${\mathrm{C}}^{3+}(1{s}^{2}2{p}_{0}$) and ${\mathrm{C}}^{3+}(1{s}^{2}2{p}_{1}$) is also discussed to interpret the differences observed between their respective differential cross sections.

Single- and Double-Electron Capture Processes in Low-Energy Collisions of N4+ Ions with He**Supported by the National Natural Science Foundation of China under Grant Nos. 11774344, 11474033 and 11574326, and the National Key Research and Development Program of China under Grant No. 2017YFA0402300.

We investigate the electron capture processes of N4+(1s22s) colliding with He(1s2) in the energy range of 10–1700 eV/amu using the quantum-mechanical molecular-orbital close-coupling (QMOCC) method. Total and state-selective single-electron capture and double-electron capture (SEC and DEC) cross sections are obtained and compared with other available studies. The results agree better with the experimental data in both trend and magnitude when the electron translation factor (ETF) effects are included. Our results indicate that both the SEC and DEC processes play important roles in the considered energy region. For the SEC processes, the N3+(1s22p2) + He+(1s) states are the dominant capture states, and the N2+(1s22s2p2) + He2+ states are the main DEC states.

State-selective single electron capture in slow O 6+-He collisions

SynopsisThe state-selective single-electron capture processes were measured by cold-target recoil-ion momentum spectroscopy in O 6+-He collisions between 18keV and 96keV. From the longitudinal momentum spectrum of recoil ions, the single electron captured into n=3 states of projectile ion is predominant and n=4 states have a small contribution. The oscillation structure of angular differential cross sections was observed. The present experimental results are compared with other experiments at low energy and the predictions of the molecular Columbic barrier model.

Electron capture, excitation and ionization in H+–Be+ collisions

State-selective single electron capture, excitation and ionization processes in proton collisions with Be+(1s22s) and Be+(1s22p) ions are studied by using the quantum-mechanical molecular orbital (QMOCC) and the two-center atomic orbital close-coupling (TC-AOCC) methods in the combined energy range 0.01–300 keV/u. In the QMOCC calculations six 2Σ+ and three 2Π states are included in the expansion basis. The TC-AOCC expansion basis includes 35 discrete states centered on the proton and 182 states on Be2+ out of which 88 are continuum pseudostates. The atomic states on Be2+ are generated by a one-electron model potential for the electron interaction with Be2+ ion core that reproduces the exact energies with accuracy better than 0.5%. Total and state-selective electron capture and excitation cross sections to final states with n ≤ 4 are presented. The sum of the cross sections for the transitions to continuum pseudostates (ionization cross section) is also reported for both initial target states. The physical mechanisms involved in the dynamics of considered processes are discussed in detail at both low and high energies. The reported cross sections should be useful in the kinetic modeling and diagnostics of edge plasmas in present magnetic fusion experiments, as well as in the current ITER design, in which beryllium is used as first wall material.

Electron capture and excitation in He+–He(1s2s1,3S) collisions

State-selective single-electron capture and excitation processes in collisions of He+ ions with metastable He(1s2s1,3S) excited atoms are investigated by using the two-center atomic orbital close-coupling method in the energy range 0.5–100 keV/u. The expansion basis includes all the states with n ≤ 9, lmax = 4 on the projectile and all the states with n ≤ 5, lmax = 4 on the target, when treating the electron capture and vice versa, when treating the ionization. One-electron model potentials for the singlet and triplet series of states have been used that reproduce the exact energies within an accuracy of 1%–2%. Spin-resolved electron capture and excitation cross sections to nl final states with n ≤ 4 are presented. The origin of differences in the magnitude and energy behavior of spin-resolved cross sections is discussed. The reported cross section results should be useful in the studies of properties of various laboratory and astrophysical helium plasmas.

Single- and double-electron transfer in low- and intermediate-energy C4+ + He collisions

The electron-capture processes in ${\mathrm{C}}^{4+}$ + He collisions have been studied theoretically using a two-active-electron semiclassical atomic-orbital close-coupling method in a wide energy domain. The results of the present calculations are compared with available theoretical predictions and experimental measurements: very good agreements are found for both total and state-selective single-electron-capture (SEC) and double-electron-capture (DEC) cross sections. We extend the understanding on that system to high energies for which only a single series of data exists. Furthermore, the mechanisms responsible for SEC and DEC processes have been investigated by additional restricted two-active-electron and single-active-electron calculations. The role of electronic correlations in the collisions is also discussed.

Experimental investigation of state selective single-electron capture in 120 keV Ar8+ - He collisions

SynopsisThe longitudinal and the transversal momentum of recoil ions were measured for single electron capture in 120 keV Ar8+ - He collisions, using the reaction microscope techniques. The characteristics of the radial and the rotational coupling were identified for 1s to 4s and 1s to 4p sub-state selectivity.

State-selective electron capture in He++ H2collisions at intermediate impact energies

State-selective single electron capture in collisions of He${}^{+}$ with H${}_{2}$ molecules is investigated using the cold-target recoil-ion momentum spectroscopy technique. The energy range considered is 6.25 keV/amu (projectile velocity ${v}_{p}$ $=$ 0.5 a.u.) to 50 keV/amu (${v}_{p}$ $=$ 1.41 a.u.). In addition, we explore the transverse recoil momentum distributions that provide direct access to the angular scattering of the receding projectile. The present experimental data are contrasted to the theoretical results obtained by means of the classical trajectory Monte Carlo model with which we find good overall agreement in the energy range explored.

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

Polarization Degrees for 3p 2P3/2–3s 2S1/2 Transition of C3+ (1s23p) Produced in Collisions of C4+ with He and H2

Charge transfer processes in collisions of C 4+ with ground-state He and H 2 are investigated using the two-center atomic orbital close-coupling method. Total and state-selective single-electron capture cross sections are obtained for collision energies between 1 and 7 keV/amu, and comparison with available experimental data reveals a good agreement. The polarization degrees for the 3 p 2 P 3/2 –3 s 2 S 1/2 transition of C 3+ (3 p 2 P 3/2 ) are calculated from the magnetic substate-selective cross sections, in which the cascade effects are also included. The polarization degree in the C 4+ +H 2 collisions varies smoothly in the considered energy region and generally agrees with the experimental measurements, while if appears minimum at a collision energy of 2 keV/u for C 4+ +He collisions. By studying the time-evolution of electron capture dynamics in the two systems we have found that the polarization difference between the two systems is caused mainly by interactions at relatively small internuclear dis...

State-selective single electron capture studied for C4+ ions on H2 at 40 keV

The experiment on state-selective single electron capture process of C4+ ions with molecular hydrogen at 40keV was performed by reaction microscope. The differential cross sections have been obtained by measuring the longitudinal and transverse momentum of recoil ions. The results show that single electron capture into M shell is by far the dominant reaction channel. The results can be qualitatively understood by reaction window of molecular coulomb barrier model.

State-selective single-electron capture in slow collisions of Neq+ (q = 2 – 5) ions with H2O

State-selective differential cross sections for single-electron capture processes in very slow collisions of Neq+ (q=2–5) ions with H2O have been studied experimentally at laboratory impact energies between 15 and 100 qeV and scattering angles between 0° and 8° by means of the translational energy-gain spectroscopy technique.

Low-energy electron capture in collisions ofC3+with He

Charge transfer processes due to collisions of ground-state ${\text{C}}^{3+}(1{s}^{2}2s\text{ }^{2}S)$ ions with He atoms are studied using the quantum-mechanical molecular-orbital close-coupling method for energies in the range ${10}^{\ensuremath{-}4}--2\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{eV}/\text{u}$. The ab initio adiabatic potentials and radial couplings utilized in the calculations are obtained from the multireference single- and double-excitation configuration interaction approach. Total and state-selective single-electron capture cross sections and rate coefficients are calculated and compared with the available experimental and theoretical data. A good agreement is found between the measured cross sections and the present calculations. However, the previous calculations of total rate coefficients using the Landau-Zener model are one to two orders of magnitude smaller than the present results.

Experimental differential investigation of state-selective single electron capture in slow He2+-He collisions

State-selective single electron capture in He2+-He collisions at energies ranging from 20 to 40 keV have been studied experimentally by means of cold target recoil ion momentum spectroscopy. The differential cross sections have been obtained by measuring the longitudinal and transverse momenta of recoil ions. The results show that single electron capture into L shell is the dominant reaction channel, which was qualitatively explained with reaction window theory. The measured state-selective cross sections agree with the semi-classical close-coupling calculations, but have some deviations from the results of photon emission measurement. Total angular differential cross sections show that the single electron capture into ground state mainly contributes at small angles, and the single electron capture into excited states contributes at large angles. The oscillating structures of angular differential cross sections are observed, and can be understood by the interference of molecular orbits during the collision processes. The measured angular differential cross sections are compared with other experiments and the quantum-mechanical calculation.

Charge transfer and ionization in collisions ofSi3+with H from low to high energy

Charge transfer processes due to collisions of ground state ${\mathrm{Si}}^{3+}(3s\phantom{\rule{0.3em}{0ex}}^{1}S)$ ions with atomic hydrogen are investigated using the quantum-mechanical molecular-orbital close-coupling (MOCC) and classical-trajectory Monte Carlo (CTMC) methods. The MOCC calculations utilize ab initio adiabatic potentials and nonadiabatic radial coupling matrix elements obtained from Herrero et al. [J. Phys. B 29, 5583 (1996)] which were calculated with a full configuration-interaction method. Total and state-selective single-electron capture cross sections are obtained for collision energies from $0.01\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{u}$ to $1\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\mathrm{u}$. Total and state-selective rate coefficients are also presented for temperatures from $2\ifmmode\times\else\texttimes\fi{}{10}^{3}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ to ${10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Comparison with existing data reveals that the total CTMC cross sections are in good agreement with the experimental measurements at the higher considered energies and that previous Landau-Zener calculations underestimate the total rate coefficients by a factor of up to two. The CTMC calculations of target ionization are presented for high energies.

State-Selective Electron Capture for keV He2+ Ions onHelium Collisions Studied by Recoil Momentum Spectroscopy

State-selective single electron capture cross sections are measured byrecoil ion momentum spectroscopy technique for He2+ on He at30 keV incident energy. The cross sections for capture into ground andexcited states are obtained and compared to classical modelcalculations as well as to the quantum mechanical calculations. Theexperimental results are in good agreement with quantum mechanicalresults.

State selective single-electron capture in O6+ + Na collisions

Single-electron capture in O6+ + Na collisions at 1–9 keV/amu collision energy has been studied both experimentally and theoretically. Partial cross sections for electron capture into n = 5, 6, 7, 8 and n ⩾ 9 have been obtained from target recoil momenta measured by the technique of MOTRIMS and are compared with close-coupling results obtained from a two-centre extension of the basis generator method. An overall good agreement is found, concerning the relative magnitude as well as the energy dependence. Also the contribution of ionization could be extracted from the recoil spectra. The ionization cross section is very small but strongly increases with energy.

State-selective single-electron capture by Ar4+ and Ar5+ ions from N2, O2 and CF4 molecules

Single-electron capture processes in collisions of Arq+ ions with N2, O2 and CF4 have been studied experimentally at laboratory impact energies of 50qeV (q=4 and 5, where q is the projectile charge state) and scattering angles between 0° and 6° by means of a translational energy-gain spectroscopy technique. The translational energy-gain spectra show that the dominant reaction channels are due to non-dissociative single-electron capture into excited states of the projectile product Ar(q−1)+. However, at large scattering angles, other channels due to transfer excitation processes start to contribute significantly. The spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the Landau–Zener model and the extended version of the classical over-the-barrier model.