State-selective Charge Exchange Research Articles

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.

Strongly perturbed state-selective charge exchange between slowAr8+and He

We report an experimental and theoretical study of state-selective charge exchange processes in ${\mathrm{Ar}}^{8+}$ on He collisions at 1 and 3 keV/amu, benchmarking the fundamental electron capture dynamics under strong perturbations. The quantum-state selectivity has been experimentally resolved for one $1s$ electron of He capture into $4s$, $4p$, $4d+4f$, and $5s$ states of ${\mathrm{Ar}}^{7+}$ ion along with the corresponding scattering angle differential cross sections. By comparing to theoretical calculations with a two-active-electron semiclassical asymptotic-state close-coupling approach, we are able to verify the important role of electronic correlations during the collisions and that the impact parameter sensitive transition probability significantly mediates the state-selective specifics.

State-selective Charge Exchange in 19.5–100 keV amu−1 O6+ Collision with He and H2

The cross sections of state-selective charge exchange (CX) between highly charged ions and neutrals are important for modeling extreme ultraviolet and soft X-ray emissions in many astrophysical objects with hot plasma impacting cold media. By using cold-target recoil-ion momentum spectroscopy, we measure O6+ CX collisions with He and H2 in the collision energy range of 19.5 to 100 keV amu−1. The relative cross sections of state-selective single CX are reported for electron capture into O5+(1s 2 nl) n = 2, 3, 4, 5, ≥6 and n = 3, 4, 5, ≥6 for He and H2, respectively. With the collision energy increasing to 100 keV amu−1, the main capture channel shifts to higher n for both target species as compared to available theoretical results. We also report state-selective cross sections for double CX with He, where doubly excited states of with being 2s 2 (1S), 2s2p (1P), 2p 2 (1D), and 2p 2 (1S) [symmetric configurations] and 2s3l, 2p3l−2s4l, and 2s5l−2p5l [asymmetric configurations] are distinguished. It is found that the contributions of doubly excited states with asymmetric configurations are dominant and symmetric configurations increasingly come into play with the increase of collision energy. The present results provide experimental benchmarks available for theoretical calculations.

Measurement of n- and l-resolved State-selective Charge Exchange in Ar8+ Collision with He

The state-resolved capture cross sections for principal n and orbital angular momentum l play an important role in modeling soft X-ray emissions induced by charge exchange for many astrophysical environments. However, the empirical and semiclassical theories used to produce these data of n- and l-resolved state-selective capture have not been well tested. Using the cold target recoil ion momentum spectroscopy apparatus at Fudan University, we perform a series of measurements of Ar8+ ion charge exchange with He in the collision energy range from 1.4 to 20 keV u−1. We find that electrons are mainly captured in the n = 4 state of Ar7+ ions. This agrees with the prediction of the scaling law for n capture. Moreover, the relative cross sections are reported for 4s-, 4p-, 4d-, and 4f-resolved state-selective capture. The often used analytical l distributions in the astrophysical literature are evaluated by comparing to the measurements.

State-selective charge exchange cross sections in Be^{4+} -hbox {H}(2textit{lm}) collision based on the classical trajectory Monte Carlo method

A three-body classical trajectory Monte Carlo method is used to calculate the nl state-selective charge exchange cross sections in hbox {Be}^{mathrm {4+}}+ H(2lm) collisions in the energy range between 10 and 200 keV/amu. We present partial cross sections for charge exchange into hbox {Be}^{mathrm {3+}}(nl) (textit{nl} = 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f) states as a function of impact energy. Our results are compared with the previous classical and quantum-mechanical results. We show that the classical treatment can able to describe reasonably well the charge exchange cross sections.Graphic abstract

Measurement of n-resolved State-selective Charge Exchange in Ne(8,9)+ Collision with He and H2

Abstract Charge exchange between highly charged ions and neutral atoms and molecules has been considered as one of the important mechanisms controlling soft X-ray emissions in many astrophysical objects and environments. However, for modeling charge exchange soft X-ray emission, the data of n- and l-resolved state-selective capture cross sections are often obtained by empirical and semiclassical theory calculations. With a newly built cold target recoil-ion momentum spectroscopy (COLTRIMS) apparatus, we perform a series of measurements of the charge exchange of Ne(8,9)+ ions with He and H2 for collision energy ranging from 1 to 24.75 keV/u. n-resolved state-selective capture cross sections are reported. By comparing the measured state-selective capture cross sections to those calculated by the multichannel Landau–Zener method (MCLZ), it is found that MCLZ calculations are in good agreement with the measurement for the dominant n capture for He target. Furthermore, by using nl-resolved cross sections calculated by MCLZ and applying l distributions commonly used in the astrophysical literature to experimentally derived n-resolved cross sections, we calculate the soft X-ray emissions in the charge exchange between 4 keV/u Ne8+ and He by considering the radiative cascade from the excited Ne7+ ions. Reasonable agreement is found in comparison to the measurement for even and separable models, and MCLZ calculations give results in a better agreement.

Experimental measurement of state-selective charge exchange and test of astrophysics soft X-ray emission model

Charge exchange, or electron capture, between highly charged ions and atoms and molecules has been considered as one of important mechanisms controlling soft X-ray emissions in many astrophysical objects and environments. However, to model charge exchange soft X-ray emission, astrophysicists commonly use principal quantum number <i>n</i> and angular momentum quantum number<i>l</i> resolved state-selective capture cross section data, which are usually obtained by empirical and semi-classical theory calculations. The accuracy of the theoretical model is the key to constructing an accurate X-ray spectrum. With a newly-built cold target recoil ion momentum spectroscopy apparatus, we perform a series of precise state-selective cross section measurements on Ne<sup>8+</sup> ions’ single electron capture with He targets, with the projectile energy ranging from 1.4 to 20 keV/u. The experimentally measured Q value spectrum shows that the process of electron captured to state of Ne<sup>7+</sup> with <i>n</i> = 4 is the main reaction channel, and that with <i>n</i> = 3 and 5 are the small reaction channels. Using Gaussian curve to fit the area of each channel on the Q value spectrum and normalizing the area of all channels, we obtain the <i>n</i>-resolved relative state-selective cross section. By comparing the measured relative cross sections with the results calculated by the multichannel Landau-Zener method and molecular Coulomb over-barrier model, significant difference among the strengths of small reaction channels is found. Specifically, the multichannel Landau-Zener method overestimates the contribution of <i>n</i> = 2 channel and <i>n</i> = 3 channel, and underestimates the contribution of <i>n</i> = 5 channel. The molecular Coulomb over-barrier model overestimates the contribution of <i>n</i> = 5 channel and underestimates the contribution of <i>n</i> = 3 channel. The significant difference between the theoretical model calculation and experimental measurement is due to the limitations of semiclassical theoretical method and classical theoretical method. Furthermore, with <i>l</i> distribution models commonly used in the astrophysical literature, including the statistical model, separable model, Landau-Zener-I model, Landau-Zener-II model and even model, we calculate the soft X-ray emissions in the charge exchange between 1.6 and 2.4 keV/u Ne<sup>8+</sup> and He. It is found that the calculated intensities of X-ray spectra significantly deviate from the existing measurements, and only the separable model can partly match the laboratory simulated solar wind charge exchange X-ray measurement. Furthermore, we find that the intensity of the charge exchange X-ray emission spectrum measured experimentally is dependent on the collision energy, while the emission spectrum calculated based on the model seems to be unchanged with the increase of the collision energy. These results indicate that if the classical and semi-classical models are applied to the astrophysical plasma for studying diffusive soft X-ray background, the obtained parameters of the astrophysical plasma will be inaccurate.

Strong sensitivity of x-ray emission lines following charge exchange between highly charged ions andH(1s)in weakly screened media

Fil: Cariatore, Nelson Daniel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Instituto de Fisica del Sur. Universidad Nacional del Sur. Departamento de Fisica. Instituto de Fisica del Sur; Argentina

Scaling for state-selective charge exchange due to collisions of multicharged ions with hydrogen

In this article we evaluate state-resolved charge exchange cross sections for Be and projectiles colliding with atomic hydrogen employing two different methods: the classical trajectory Monte Carlo and the eikonal impulse approximations. These cross sections are used to extend previously derived scaling laws for n-, nl-, and nlm-distributions to highly excited final levels with covering energies in the range amu. Present total and partial capture cross sections are in agreement with available experimental and theoretical data for these collision systems. Besides, the proposed scaling rules are also verified by other theories, becoming a useful instrument for plasma research.

Scaling for state-selective charge exchange due to collisions of multicharged ions with hydrogen

SynopsisState-resolved charge exchange (CX) cross sections for Be4+, C6+, N7+ and O8+ projectiles colliding with atomic hydrogen are evaluated employing two different methods: the Classical Trajectory Monte Carlo (CTMC) and the eikonal impulse (EI) approximations. These cross sections are used to extend previously derived scaling laws for n−, nl−, and nlm− distributions to highly excited final levels with 4 ≤ n ≤ 9, covering energies in the range 50-2000 keV/amu. Present results are in agreement with available experimental and theoretical data for these collision systems, becoming a useful instrument for plasma research.

Recoil-ion momentum spectroscopy for He2+ + He electron capture reactions

Electron capture reactions for 3He2+ collisions on He at impact energies in the range 40 keV-300 keV have been studied using the Cold Target Recoil-Ion Momentum Spectroscopy setup which has recently became operational at the Centro Atomico Bariloche. State-selective charge exchange cross sections were obtained and in this work we present recoil-ion transverse momentum distributions. For targets with residual thermal motion, we show that the implementation of a back-projection algorithm based on the transverse momentum distribution component along a direction perpendicular to the jet direction provides results in agreement with those obtained by using previously cooled targets. Present results nicely fit the gaps in the datasets already published by other laboratories and are found to be in good agreement with classical trajectory Monte Carlo simulations.

Calculation of ionization and total and partial charge exchange cross sections for collisions of C6+ and N7+ with H

We have performed calculations for collisions between fully stripped ions, C6+ and N7+, and atomic hydrogen, in both its ground and first excited energy levels. We have employed the Classical Trajectory Monte Carlo method to obtain total ionization and charge exchange cross sections and state selective charge exchange cross sections in the 5–500 keV/amu energy range.

Development and evaluation of a many-electron–multicenter classical-trajectory Monte Carlo model in charge-exchange processes involving collisions of multiply charged ions and CO

A many-electron--multicenter classical-trajectory Monte Carlo model is developed and tested in charge-exchange studies involving projectiles with charges from $+$3 to $+$10 and the CO molecule. The present model is contrasted against simpler single-center and independent-atom approaches. Total and state-selective charge-exchange cross sections are presented and are compared to recent data from the Jet Propulsion Laboratory where available.

State-selective charge exchange in slow collisions of Si3+ ions with H atoms: A molecular state close coupling treatment*)

Charge transfer cross sections are calculated by employing both the quantal and semiclassical ε(R) molecular orbital close coupling (MOCC) approximations in the adiabatic representation and compared with other theoretical and experimental results

Evidence of electron saddle swap oscillations in angular differential ion–atom charge exchange cross sections

State selective charge exchange processes in 1–10 keV/amu Ne8+ +Na(3s) collisions were measured by means of the magneto-optical trap recoil-ion momentum spectroscopy technique and compared to classical trajectory Monte Carlo calculations. We find that for electron capture to n-levels ≥ 10, the transverse momentum distributions exhibit an oscillatory structure which is very sensitive to the impact energy. Our theoretical analysis suggests that this feature is a direct consequence of the number of swaps the electron undergoes across the potential energy saddle during the charge exchange process.

State-selective charge exchange from Na(3s) and Na*(3p) by highly charged ions

State-selective charge exchange cross sections and momentum spectra are calculated for collisions of Xe18+ and Xe54+ ions with Na(3s) and Na*(3p) over the energy range of 0.1–10.0 keV/amu. The classical trajectory Monte Carlo method is used which includes all two-body interactions. The n-level cross sections are found to be rather insensitive to collision energy below 1 keV/amu. In contrast, the transverse momentum cross sections for specific n-levels change rapidly with energy. However, this latter variation in energy is found to be in general agreement with simple scaling rules. Experimental state-selective data are available for Xe18+ over a limited energy range; they are found to be in reasonable accord with the calculations.

State-selective charge exchange from H(1s), H(n = 2), Li and Na targets by very highly charged ions

In order to provide information for charge exchange spectroscopy diagnostics in new, high temperature tokamak plasmas, n-level state-selective electron capture cross sections are presented for very highly charged ions with charge states q ⩾ 10. Fully stripped ions with charges of 10+, 18+, 26+, 54+ and 92+ are considered in order to provide scaling information over a broad range. The H(1s) and H(n = 2) targets are evaluated at 1, 10 and 100 keV/amu, i.e. plasma core temperatures to those encountered during neutral beam heating. For use in pellet diagnostics, cross sections are given for Li and Na targets at 10 keV/amu. These latter targets also provide a means to experimentally test the accuracy of the H(n = 2) results since they are pseudo-one-electron atoms with ionization energies close to that of excited hydrogen.

Charge Exchange Emission from Solar Wind Helium Ions

Charge exchange X-ray and far-ultraviolet (FUV) aurorae can provide detailed insight into the interaction between solar system plasmas. Using the two complementary experimental techniques of photon emission spectroscopy and translation energy spectroscopy, we have studied state-selective charge exchange in collisions between fully ionized helium and target gasses characteristic of cometary and planetary atmospheres (H2O, CO2, CO, and CH4). The experiments were performed at velocities typical for the solar wind (200-1500 km s-1). Data sets are produced that can be used for modeling the interaction of solar wind alpha particles with cometary and planetary atmospheres. These data sets are used to demonstrate the diagnostic potential of helium line emission. Existing Extreme Ultraviolet Explorer (EUVE) observations of comets Hyakutake and Hale-Bopp are analyzed in terms of solar wind and coma characteristics. The case of Hale-Bopp illustrates well the dependence of the helium line emission to the collision velocity. For Hale-Bopp, our model requires low velocities in the interaction zone. We interpret this as the effect of severe post-bow shock cooling in this extraordinary large comet.

Ultrasensitive radioactive detection of collinear-laser optical pumping: Measurement of the nuclear charge radius of 2Ca.

We report the first application of an ultrasensitive detection scheme in on-line collinear-laser spectroscopy. It is based on radioactive detection of optical depopulation pumping, using state-selective charge exchange as an intermediate step. This extends the calcium isotope shift measurements beyond the ${\mathit{f}}_{7/2}$ shell closure. The extracted $^{50}\mathrm{Ca}$ mean-square charge radius constitutes the first experimentally determined one of a short-lived neutron-rich isotope beyond the N=28 shell closure. The steep increase in radius after the doubly magic $^{48}\mathrm{Ca}$ nucleus indicates a strong coupling between the ${\mathit{p}}_{3/2}$ neutrons and the core protons.

Effects of state-selective charge-exchange processes on the He-like spectra from the Alcator C tokamak.

The effects of a low-energy charge-exchange process between hydrogenlike ions and neutral hydrogen on x-ray spectra of He-like argon ions from the Alcator C tokamak are investigated. Dependences of charge-exchange cross sections on both the principal and angular momentum quantum numbers n and l are estimated from the observed spectra, taking cascade effects into account with the use of a collisional radiative model.