T K McLaughlin

Importance of dissociative excitation by slow He2+ ions in one-electron capture collisions with H2

Translational energy spectroscopy has been used to study one-electron capture by 0.5-2.0 keV amu-1 He2+ ions in collision with H2. The main excited state product channels have been identified and the relative cross sections determined. These measurements provide the first direct evidence of the relative importance of dissociative excitation channels in electron capture (with He+ formed in the ground state and H atoms mainly in the n=2 states) which dominate the entire energy range. Non-dissociative electron capture into the n=2 and n=3 states of He+, which is also observed, increases from 1% of the total electron capture cross section at 0.5 keV amu-1 to about 25% at 2 keV amu-1.

State-selective electron capture by slow N4+ ions in collisions with helium

Translational energy spectroscopy in an apparatus previously developed in this laboratory has been used to study one-electron capture by 4-28 keV N4+ ions in collisions with helium. The main excited N3+ product channels have been clearly identified and the relative cross sections determined. The two main channels are found to involve core rearrangement. While the N3+ 2p2 1 S product channel is dominant, it is shown that other channels involving large energy defects contribute significantly at the higher energies thereby resulting in an essentially energy invariant total one-electron capture cross section: MCLZ calculations, which have also been carried out, satisfactorily predict the main 2p2 1 S product channel but fail to account for the other channels arising from curve crossings at small internuclear separations.

State-selective one-electric capture by 8 keV He2+ ions in collisions with oxygen atoms

The authors have successfully demonstrated the feasibility of using translational energy spectroscopy with partially dissociated oxygen within an iridium tube furnace to provide, for the first time, data on state-selective one-electron capture in collisions of 8 keV He2+ ions with ground state atomic oxygen. Near-resonant electron capture into the He+ (n=2) states is the dominant collisional channel. Cross sections for the main excited product channels in one-electron capture in collisions of He2+ with both O and O2 have been estimated from an analysis of the observed energy change spectra; the total cross section for one-electron capture by He2+ in O has also been determined.

State-selective electron capture by slow S3+ recoil ions in H, H2 and He

Translational energy spectroscopy has been used to study electron capture by slow S3+ ions from a recoil ion sources. These ions are important in astrophysical plasmas. Cross sections for state-selective electron capture by S3+ ions in H, H2 and He have been determined at energies within the range 2.4-9.0 keV. The main excited product channels have been identified and their relative importance has been assessed. In the case of H and He a multichannel Landau-Zener model has been used to predict cross sections which have been compared with experiment. The presence of S3+(4P) metastable as well as S3+(2P degrees ) ground-state ions in the primary beam has been clearly demonstrated. Electron capture by ground-state ions is dominated by 3p electron capture. For H and H2 the majority of channels also involve 3s to 3p excitation of the projectile core.

Study of state selective electron capture in C4+‐H collisions

Translational energy spectroscopy has been used with highly dissociated hydrogen contained within a tungsten tube furnace to identify and obtain cross sections for the main excited product channels in electron capture in C4+‐H collisions.

First observations of state selective electron capture by multiply charged ions in collisions with atomic oxygen

Translational energy spectroscopy has been used to study state‐selective electron capture by multiply charged ions in partially dissociated oxygen contained within an iridium tube furnace. Having recently obtained data on He2+–O collisions using this approach, we have now used a similar approach to study C4+–O collisions and identify the main collision channels.

State selective two‐electron capture by C4+ ions in collisions with helium

Translational energy spectroscopy has been used to study two‐electron capture in C4+‐He collisions at energies within the range 4–12 keV. The main excited product channels have been identified, quantitatively assessed and compared with MCLZ calculations and other relevant data.

State selective one and two‐electron capture in collisions of C4+ ions with Ne

Translational energy spectroscopy has been used to study both one and two‐electron capture in C4+‐Ne collisions within the range 4–16 keV. The main excited product channels have been identified and the relative yields compared with our MCLZ predictions.

First measurements of state-selective one-electron capture by 4–24 keV N4+ ions in H and H2

Translational energy spectroscopy has been used in conjunction with a tungsten tube furnace target to study state-selective one-electron capture by 4–24 keV N4+ ions in collisions with both H and H2. The main N3+ excited product channels have been identified and, in the case of H, the corresponding cross-sections have been determined and shown to be in reasonable agreement with one recent theoretical prediction.

State-selective electron capture in collisions of slow Fe3+ and Fe4+ ions with H and He atoms

Translational energy spectroscopy in an apparatus previously developed in this laboratory has been used to study state-selective one-electron capture by Feq+ (q=3, 4) ions in collisions with He and H at energies of q*2 and q*4 keV. The data, which are the first of their type, are relevant to a better understanding of the plasma edge and neutral beam heating and diagnostics in fusion energy devices. The main excited products are shown to arise through electron capture-into n=3 and n=4 states. Electron capture by Fe3+ ions is shown to be dominated by many collision channels involving metastable ions which preclude a detailed analysis. In contrast, observed energy change spectra for Feq+ impact can be satisfactorily interpreted in terms of a predominant contribution from collision channels involving ground state primary ions. MCLZ calculations have also been carried out and compared with experiment for both Fe4+-He and Fe4+-H collisions.