S.M. Ferguson

Experimental study of single-electron capture by low-energy Neq+ recoil ions (q=3-6) from He, Ne and Ar using translational energy spectroscopy

The translational energy spectroscopy technique has been used to study single-electron capture processes for collisions of slow Neq+ ions (q=3-6, where q is the projectile charge state), produced in a recoil ion source, with He, Ne and Ar at laboratory impact energies between 100 and 600 eV and scattering angles between 0 degrees and 6 degrees . The measurements show that the dominant reaction channels are due to capture into excited states of the projectile products and show a dependence on scattering angle. There is clear evidence of the presence of the first and second metastable states in the incident Ne3+ ion beam. A reasonable description of the dominant final states is obtained in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model. The measured differential cross sections show that the projectile products are distributed with maximum intensity near a scattering angle theta c which corresponds to capture at an impact parameter equal to the crossing radius.

Transfer ionization in 0.5–1.5 MeV/u O5–8+ + He collisions

Transfer ionization (TI), in which electron capture is accompanied by loss of the other electron from the target, been measured for 0.5 to 1.5 MeV/u 0/sup q//sup +/ ions (q = 5-8+) colliding with helium. These new measurements, in conjunction with previous measurements at lower energies, are used to formulate a scaling rule to describe the projectile energy and charge state dependences of TI for collisions involving helium targets. 10 refs., 2 figs.

Cusp-electron production in intermediate-energy O7+ + Ar collisions

Abstract Cusp-electron production has been investigated in 0.5–1.5 MeV/u O7+ + Ar collisions. For this system, cusp electrons can result from electron capture or loss to the continuum (ECC or ELC), transfer ionization (TI), or double transfer ionization (2TI). Of particular interest are the two- and three-electron processes TI and 2TI. The ratios TI ECC and 2TI ECC each exhibit a maximum near 0.75 MeV/u, while the ELC ECC ratio increases monotonically with beam energy. The reasons for these behaviors, including electron correlation effects, are considered.

Differential scattering of low‐energy Ne4+ recoil ions from He and Ar associated with capture

A differential energy‐gain spectrometer, capable of measuring simultaneously the scattering angle and the energy‐gain of projectile products in ion‐atom collisions, has been used for the study of state‐selective single‐electron capture from He and Ar by Ne4+ ions produced in a recoil ion source at laboratory impact energies between 100 and 400 eV and scattering angles between 0° and 5°. For Ne4+‐He and Ne4+‐Ar collisions the dominant reaction channels are due respectively to capture from the ground state 2p23P of Ne4+ ions into excited states 3s 4P and 3d 2P of Ne3+.

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

SINGLE-ELECTRON CAPTURE IN LOW-ENERGY AR6+-HE COLLISIONS

Double differential cross sections for state-selective single-electron capture processes in Ar6+-He collisions have been measured at laboratory energies between 75 and 900 eV and scattering angles between 0 and 8°. At the lowest energy, the zero-angle spectrum shows capture into Ar5+(4p) to be the most important channel. However, as the scattering angle is increased, a second peak appears at angles ≥2° and becomes more pronounced relative to the 4p capture channel. The energy spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model. Total and differential cross sections are also measured and compared with available measurements and calculations.

Differential single-electron capture cross sections in low-energy Arq+ (q = 4–8) ions — He and Ar collisions

Abstract Differential cross sections for single-electron capture by Arq+ ions (q = 4–8) from He and Ar have been measured at impact energies between 600 and 2500 eV, and projectile scattering angles between 0 and 25 mrad. The experimental angular distributions contain a main peak lying near a critical angle θc, which corresponds to capture at an impact parameter equal to the crossing radius. The results are quantitatively explained by a semi-classical model based on Coulomb potential energy curves.

Differential cross sections for single-electron capture processes by low-energy multiply charged ions

Abstract Doubly differential cross sections, in energy and angle, for state-selective single-electron capture by Ne3+, Ne4+ ions from Ne, and Ne6+ ions from He have been measured at laboratory impact energies between 60 and 600 eV and scattering angles between 0° and 5°. The measurements show that the angular distributions of the reaction channels with large energy-gain values are shifted towards larger scattering angles as would be expected. The energy-gain spectra are interpreted qualitatively in terms of the reaction window, which are calculated using the single-crossing Landau-Zener model.

Translational energy spectra and differential cross sections for low-energy Ar5+-Ar and Ne5+-Ne collisions

Abstract Translational energy spectra and differential cross sections for state-selective single-electron capture processes in low-energy Ar 5+ -Ar and Ne 5+ -Ne collisions have been measured at laboratory impact energies between 125 and 500 eV and scattering angles between 0° and 5°. Translational energy spectra indicate that the dominant reaction channels are due to capture into excited states of the projectile products and show an impact parameter dependence. The measured differential cross sections show that the projectile products are distributed near a scattering angle θ c corresponding to capture at an impact parameter equal to the crossing radius.

Transfer ionization in ion collisions with helium

Abstract The two-electron process of transfer ionization (TI) is considered for ions in the energy range 0.1–2.5 MeV/u colliding with helium targets. Of interest are the mechanisms responsible for TI over this range, and the role, if any, played by the electron-electron interaction in the high-velocity limit. Results obtained from new measurements for He+ and Oq+ ions are compared with previous results from other investigators. For velocities from about 0.1 MeV/u to > 1 MeV/u TI appears primarily due to independent capture and ionization events. From the available data, it is not possible to determine if the expected electron correlation effects dominate at very high velocity (≥ 10 MeV/u).