Projectile Charge State Research Articles

Single- and multiple-charge changing cross sections in slow collisions of Arq+ (q = 4−9) with Ne

Single- and multiple-charge changing cross sections of Arq+ (q = 4−9) in collisions with Ne have been measured at very low impact energies ranging from 0.0125 · q to 25 · qeV/amu, systematically. The single-charge changing cross sections have relatively weak energy dependence and their averages increase with increasing charge state of projectiles roughly in agreement with a scaling law developed by Müller and Salzborn. Multiple-charge changing cross sections strongly depend on the collision energy and have a minimum structure being in terms of the projectile charge q and the charge change. Single-charge changing cross sections are well reproduced by the multi-cross Landau-Zener calculation taking the attractive induced-dipole polarization potential into consideration.

Electron capture and fragmentation in Ar11+ + CO collisions

Collisions between 32.2, 130.5 and 570.5 keV Ar11+ ions and CO molecules have been studied using the Macdonald Laboratory CRYEBIS. Coincidence time of flight was used to detect all recoil ions originating from each molecule and a position sensitive detector was used to determine final projectile charge states. Single-and double-electron capture cross-sections are much larger than those for ionization at these collision energies. The dominant recoil channel associated with the Ar10+ final charge state is the CO+ molecular ion. The main ion-pair channel is the C+ + O+ dissociation of CO2+ while the relative yields of higher charge states of the transient COq+ fall off rapidly. The dissociated ions corresponding to charge states up to CO4+ were detected in coincidence with Ar10+ (and Ar9+), indicating that multielectron capture followed by autoionization occurs.

Precise total electron yield measurements for impact of singly or multiply charged ions on clean solid surfaces

Total electron yields γ for impact of singly or multiply charged ions (H+, He+, He2+, N3+, N4+, O5+, O6+) on clean polycrystalline gold have been accurately measured at impact energies from almost zero [exclusive potential emission (PE) range] up to 40 keV times projectile charge state q (dominant kinetic emission range). Impact energies above 10 q keV have been approached by postacceleration of ions via target biasing with up to −30 kV. Total electron yields for γ⩾3 have been derived directly from the related electron number statistics (ES) with total experimental errors of ±3%. Smaller values of γ have been determined from the related ES in conjunction with measurements of the respective primary ion, and ejected-electron currents, which caused somewhat larger experimental errors of typically ±5%. At higher impact velocity discrepancies arise between results from ES-based and current-based measurements of the total electron yield, respectively, because of systematic errors of the latter method due to projectile ion reflection and/or secondary ion emission from the target surface. For differently charged ion species, a difference in γ due to the q-related PE stays almost independent of the projectile impact energy.

The ionization of helium by 1.5–7.5 MeV partially stripped C q+ ions

The double to single ionization cross section ratios of helium by partially stripped carbon ions have been measured for projectile charge states ranging from +1 to +4 and impact energies from 1.5 to 7.5 MeV. The effective charge effect in partially stripped ion-helium collision is presented. It is found that the effective charge q eff increases as the impinging energy increases and q eff shows a modest dependence upon the projectile charge state in the present energy range. The projectile charge state, projectile and target electronic state dependences of the effective charge effect is discussed using orbital interpenetrating. The nCTMC calculations were carried out to investigate the energy dependence of the effective charge. By introducing effective charge the cross section ratio of helium obtained in the present work is in good agreement with the ( V q eff ) −2 law.

Projectile velocity and target temperature dependence of charge-state distributions of multicharged ions scattered during grazing interactions with a Au(110) surface.

We have made systematic measurements of scattered projectile charge-state distributions for multicharged He, N, Ne, Na, and Ar ions grazingly incident on a Au(110) single-crystal target. For projectiles whose neutral binding energies Lie below the valence band (N, Ar, He, and Ne), observed 1+ charge fractions were small at low velocities and steeply increased above well-defined threshold velocities. However, for Na projectiles with neutral binding energy above the Fermi level, a large (about 84%) 1+ charge fraction was found. The velocity dependence of the Na neutral fraction shows a ''kinematic resonance'' due to the virtual population of electronic states above the Fermi level in the projectile rest frame. The measured sample temperature dependence of the scattered 1+ charge fraction for Ne9+ projectiles incident along the [110] surface channeling direction reveals a significant decrease in projectile neutralization once the (2X1)-(1X1) phase transition temperature of the Au(110) surface at 650 K has been reached.

0 degrees binary encounter electron production in 30-MeV Oq++H2, He, O2, Ne, and Ar collisions.

Double-differential cross sections (DDCS's) for the production of binary encounter electrons (BEE's) were measured for collisions of 30-MeV ${\mathrm{O}}^{\mathit{q}+}$ projectiles with ${\mathrm{H}}_{2}$, He, ${\mathrm{O}}_{2}$, Ne, and Ar targets with q=4--8 and an electron ejection angle of \ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{} with respect to the beam direction. Particular interest focused on (a) the evaluation of the contributions of the different electron subshells of the multielectron targets, ${\mathrm{O}}_{2}$, Ne, and Ar; (b) the study of the well-known enhancement of the BEE DDCS's with decreasing projectile charge-state q; here this dependence was tested for higher collision energies and new targets; (c) the study of the dependence of the BEE peak energy on the particular target and projectile charge state. Results were analyzed in terms of the impulse approximation, in which target electrons in the projectile frame undergo 180\ifmmode^\circ\else\textdegree\fi{} elastic scattering in the field of the projectile ion. The electron scattering calculations were performed in a partial-wave treatment using the Hartree-Fock model. Good agreement with the data was found for the ${\mathrm{H}}_{2}$ and He targets, while for the multielectron targets ${\mathrm{O}}_{2}$, Ne, and Ar only electrons whose velocity was lower than the projectile velocity needed to be included for good agreement. All measured BEE DDCS's were found to increase with decreasing projectile charge state, in agreement with other recent BEE results. The BEE peak energies were found to be independent of the projectile charge state for all targets utilized. \textcopyright{} 1996 The American Physical Society.

The effective charge effect in partially stripped ion-helium collisions

The double and single ionization cross section ratios of helium by partially stripped carbon, oxygen and fluorine ions are measured for projectile charge states ranging from +1 to +4 and impact energies from 1.5 MeV to 7.5 MeV. The effective charge effect in partially stripped ion-helium collisions is studied. It is found that the effective charge qeff increases as the impinging energy increases and qeff shows a modest dependence upon the projectile charge state in the present energy range. The projectile charge state, projectile energy, projectile and target electronic state dependences of the effective charge effect may be explained using orbital interpenetrating.

Measurements of recoil and projectile momentum distributions for 19-MeV F9+ + Ne collisions.

The collision system of 19-MeV ${\mathrm{F}}^{9+}$ on Ne has been studied using recoil and projectile momentum spectroscopy. For each event, identified by final recoil and projectile charge state, the three-dimensional momentum vector of the recoil ion and the transverse momentum vector of the projectile ion were measured. The transverse momenta of the recoil and projectile ions were found to be equal in magnitude and opposite in direction, indicating that the transverse momentum exchange is dominated by interactions between the two ion cores. The transverse momentum distributions are well described by nCTMC calculations. The longitudinal momentum distributions of the recoil ions show that a large fraction of the momentum transferred to the projectile is carried off by continuum electrons. The recoil ions are scattered slightly backward, in partial agreement with predictions of nCTMC calculations. \textcopyright{} 1996 The American Physical Society.

Multiple target ionization in collisions between highly charged ions and Ar

We have performed measurements on charge-state distributions of target ions produced in collisions of , , , , and on Ar. Charge states of Ar target ions higher than the initial projectile charge state are observed for , and . This intriguing observation seems to imply that even in low-energy collisions () of highly charged ions on gas targets excitation of the target occurs due to inner-shell electron capture. For collisions of and on Ar less than six electrons are transferred.

Effective Charge Effect in 2·0 - 7·0 MeV Partially Stripped Fq+ - Helium Collisions

The ratio of the double ionisation cross section to that of the single ionisation of helium was measured for 2�0–7�0 MeV Fq+ (q = 1,2,3,4) bombardment. The effective charge effect in partially stripped Fq+ – helium collisions is studied. It is found that the effective charge qeff increases as the impinging energy increases and that qeff shows almost no dependence upon the projectile charge state in the present energy range.

THE MAXIMUM ENERGY OF ħω INDUCED BY N+, N2+ AND N3+ IONS

The continuous X-ray of Be, Ni, and Cd targets induced by N +, N 2+, N 3+ ions were measured at the projectile energies of 50-, 70-, 100-, 150-, and 200-keV. Since the energy of the projectile is so low and the detecting limit of the detector is about one keV, the continuous X-ray would be the X-rays of nuclear and atomic bremsstrahlung (NB, AB). From the result of maximum energy of ħω. the relationship of a maximum energy ħω of below: [Formula: see text] Which indicates that the maximum energy of ħω depends on (-3/5) power of the atomic number of projectile, Zp. and on (-1/3q) power of the atomic number of target atom, Zt, and on the energy of projectile. Where q expresses the number of charge state of the projectile.

One- and two-electron processes in collisions of He with 10–500 keV/amu Beq+ (q = 2–4) and Bq+ (q = 2–5) ions

Two-center semiclassical close-coupling method is applied to study collisions of He atom by bare and multiply charged ions (Beq+ (q = 2–4) and Bq+ (q = 2–5)) in the energy range of 10–500 keV/amu. Cross-sections for one-electron processes for electron capture, excitation, ionization as well as two-electron processes for transfer excitation and transfer ionization were obtained. Dependence of cross-section on projectile energy and charge state was investigated. Our calculations provided the first systematic study for these collision systems. Comparison with the limited number of previous theoretical and experimental results was also made.

Production cross sections of recoil Ar ions in coincidence with final charge states of 2 MeV C3+ projectiles

We have measured absolute cross sections of multiple ionization in coincidence with final charge states of projectiles for collisions of C3+ ions with Ar atoms at 2 MeV. At this collision energy, the recoil ions with low charge states were mainly produced by pure ionization while capture and loss ionization were important processes for the production of recoil ions with higher charge states. In an analysis of the data, an independent-electron model was applied. The results indicate that the ionization probability of the target electron depends on the impact parameter in ionization processes, such as pure-, capture-, and loss-ionization. The obtained values were compared with calculations by a classical-trajectory Monte Carlo (nCTMC). The experimental cross sections are in good agreement with the calculated values for pure, single-capture and single-loss ionization.

Ionization and charge transfer in collisions of highly charged ions with helium at low velocity.

Ionization and charge transfer in slow collisions between highly charged projectiles and helium atoms are studied by the two-center atomic orbital close-coupling method within the independent electron approximation. The relative importance of single ionization to single capture is investigated. Our calculations show that ionization cross sections for ${\mathrm{C}}^{6+}$, ${\mathrm{N}}^{7+}$, and ${\mathrm{O}}^{8+}$ projectiles increase rapidly between v=1 and 2 a.u. The onset is dependent on projectile charge state. At a fixed velocity, ionization cross sections decrease with increasing projectile charge. It is also found that ionization and charge transfer occur at about the same impact parameter range.

Scattering Study of Single Charge Transfer in Arq+ (11 .ltoreq. q .ltoreq. 14) on Ar Collisions at 72q eV

Collisions of highly charged Ar{sup q+} ions (11 {le} q {le} 14) with neutral Ar were investigated at 72q eV laboratory energy. Energy gain spectra were measured at different scattering angles, and relative doubly differential cross sections for the Ar{sup (q-1)+} product were obtained. Odd charge state projectiles are scattered with an energy gain corresponding to a narrow range of Q values, while even charge state projectiles are scattered with energy gains associated with three different groups of Q values. This even-odd variation with projectile charge state seems to be a general feature of Ar{sup q+} on Ar scattering, but no explanation for this effect is offered at this time. Energy gain spectra measured at different scattering angles were integrated over scattering angles, and the resulting function, proportional to the Q value distribution function, reflects the density of capture states.

Statistical treatment of adsorbate effects on charge transfer in ion-surface collisions

We present a theory which describes the effects of adatoms on the resonance charge transfer in ion-surface collisions, based on the statistical method similar to that used in evaluation of the spectral line shapes in plasmas. In front of a surface covered by a submonolayer of alkali atoms, the projectile valence energy level is randomly modulated by the laterally inhomogeneous electrostatic potential of the adlayer. Depending on the surface coverage and the arrangement of adatoms, we investigate the Poisson and Gaussian limits of this random process, and show that the resulting average shift and broadening of the projectile level may influence decisively the charge transfer. Based on the Anderson-Newns Hamiltonian, we study the effects of a random adlayer on the projectile charge state in both near-normal and grazing ion-surface scattering.

Angular and charge state distributions of highly charged ions scattered during low energy surface-channeling interactions with Au(110)

We have measured scattered projectile angular and charge state distributions for 3.75 keV/amu O q+ (3 ≤ q ≤ 8) and 1.2 keV/amu Ar q+ (3 ≤ q ≤ 14) ions grazingly incident along the [110] and [100] directions of a Au(110) single crystal target. Scattered projectile angular distributions characteristic of surface channeling are observed. For both incident species, the dominant scattered charge fraction is neutral, which varies only by a few percent as a function of incident charge state. Significant O − formation is observed, which manifests a distinct velocity threshold. For incident Ar projectiles with open L-shell, the positive scattered charge fractions, while always less than about 10%, increase linearly with increasing number of initial L-shell vacancies.

Negative ion production in multicharged ion-surface interactions

Measurements are presented of energy and angular resolved reflected charge state distributions for O q+ , q = 1–7, and N q+ , q = 2–7, incident projectiles scattered from a clean A1(110) single crystal surface. The measurements were carried out at 16 keV incident ion energy, and at 1.2° grazing incidence. O − reflected ions were observed for all incident O projectile charge states. The energy loss of O − reflected particles was found to be consistently larger than for reflected O + particles, which was in turn larger than for higher reflected charge states. The magnitude of the energy loss was found to be independent of the incident projectile charge. The reflected charge state distributions were also found to be independent of the incident charge state, except when projectile K shell vacancies were initially present.

Time scales for charge equilibration of Oq+ (3

We report on measurements of scattered projectile angular and charge state distributions for 3.75 keV/amu ${\mathrm{O}}^{q+}$ $(3\ensuremath{\le}q\ensuremath{\le}8)$ ions surface channeled along the $〈1\overline{1}0〉$ direction of a Au(110) single crystal target. Projectile trajectory calculations indicate that the projectiles spend less than 30 fs within 2 \AA{} of the topmost Au surface layer. Nevertheless, almost complete charge equilibration is observed in the scattered projectile charge state distributions. It is concluded that, already at the target interface, strong screening effects are present which make possible direct capture to the projectile L and M shells in relatively large impact parameter collisions.

Backward ejected electrons produced by 1-MeV/u Oq+ (q=3-8) projectile ions colliding with argon gas.

The cross sections for ejecting electrons into a cone of half-angle [similar to]2[degree] centered on the backward direction have been measured as a function of electron energy for 1-MeV/u O[sup [ital q]+] ([ital q]=3--8) projectiles colliding with Ar. For O[sup 3+] and O[sup 4+] projectiles, the cross sections have also been measured in coincidence with exit charge states ([ital q]+1) and ([ital q]+2) of the projectile. A prominent feature in all spectra is a target [ital LMM] Auger peak. The cross sections for producing Ar [ital LMM] Auger electrons are nearly independent of projectile incident charge states. A projectile electron-loss peak is produced when the projectile brings loosely bound [ital L]-shell electrons into the collision. The shape of this peak is independent of the projectile exit charge state within experimental error. The measured electron-loss production cross sections at 180[degree] are compared with the predictions of various on-shell approximations to the impulse approximation. Peak height and position are sensitive functions of the on-shell approximation used. The predictions of the elastic scattering model agree well with the data.