T.J.M. Zouros

Anomalous q dependence of 0' binary encounter electron production in energetic collisions of Fq+ (q=3-9) with He and H2 targets

The projectile charge state dependence of binary encounter electron (BEe) production was studied at zero degrees with respect to the beam direction for collisions of 19 and 28.5 MeV F(3(sup)-or+9)+= with H2 and He targets. The measured double differential cross sections for BEe production were found to be increasingly enhanced with decreasing projectile charge state contrary to the usual screening behaviour. The relative enhancement of the BEe F8+ yields over the F9+ yields was found to be about 15% increasing to about 50% for F3+ projectiles. Plausible mechanisms are discussed; however, no theoretical explanation of this anomalous enhancement is established.

A zero-degree tandem electron spectrometer and rydberg analyzer for projectile electron studies in ion-atom collisions☆

Abstract An electron spectrometer system consisting of a tandem 45° parallel-plate spectrometer preceded by a Rydberg analyzer has been developed to study projectile electron capture, ionization and excitation by 0° spectroscopy. This system has the ability to resolve a large number of excited and continuum atomic states of the projectile and has a low kinematic line broadening. High-n Rydberg electrons are field-ionized and decelerated in an inhomogeneous-field Rydberg analyzer. The field-ionized electrons are then energy-dispersed according to n-value. The design and performance of the system is presented with some results of continuum (cusp), Rydberg, Coster-Kronig and highly resolved (ΔE/E = 0.1–0.2%) K-Auger electrons for 0.5–1.75 MeV/amu, Fq++He, Ne, H2 collisions.

High resolution studies of electron capture and excitation by 0° projectile electron spectroscopy

Abstract A tandem 45° parallel-plate electron spectrometer has been developed for high resolution electron studies of atomic collision processes using the method of 0° electron spectroscopy. High resolution projectile K-Auger electron spectra have been obtained in a state-selective study of transfer-excitation (TE) and single excitation in collisions of 4.5–33 MeV F6+ with He and H2 targets. A high resolution measurement of 9.5 MeV F7+ with He yielded preliminary information on state-selective capture to the metastable F7+ (1s2s) state. Future plans include studies of Fq+ + T (q: 6−9; T: H2, He, Ne) to determine absolute state-selective cross sections for transfer-excitation, single and double electron capture.

Forward-backward asymmetry in the inelastic scattering of electrons from highly charged ions

Energy-dependent, absolute differential cross sections for 1s2l excitation in F8+ by the scattering of quasi-free target electrons have been measured. The formation and subsequent decay of the F7+ (3lnl´) (n3) doubly excited intermediate states gives rise to a resonant inelastic scattering amplitude which is coherent with the nonresonant inelastic scattering. A strong forward-backward asymmetry was found for the inelastically scattered electrons due to the interference between these two scattering amplitudes. Close-coupling R-matrix calculations show excellent agreement with the experiment and thereby demonstrates a method for obtaining high-resolution, angle-resolved differential inelastic electron-ion scattering cross sections.

Observation of electron‐electron interaction in collisions of O5+ ions with H2 targets

Using high resolution projectile electron spectroscopy at zero degrees, we have determined projectile Auger electron spectra from collisions of Li‐like O5+ beams with H2 targets at energies between 4–32 MeV. The strongest populated Li‐Like (1s2s2p) states resulting from 1s→2p excitation and Be‐like (1s2s2p2) states resulting from Transfer‐Excitation (TE) were resolved. The production of (1s2s2p2)3D states by Resonance Transfer‐Excitation was clearly observed and compared to theory. The production of (1s2s2p)4P and 2P+ states above ∼12 MeV was found to increase sharply with projectile energy, indicating the onset of projectile excitation due to an interaction with one of the target electrons.

Electron‐electron interactions in K‐shell excitation of F6+ ions in fast collisions with H2 targets

K‐shell excitation of F6+(1s22s) projectile ions in collisions with H2 targets has been studied by measuring 0° state‐resolved Auger electron production cross sections in the projectile energy range of 0.25 to 2 MeV/u. Projectile 1s→2p excitation due to the interaction with a ‘‘target electron’’ (electron‐electron Excitation1 [eeE]) has been observed in the production of the 1s(2s2p3P)2P− and 1s(2s2p1P)2P+ states as well as 1s2s2p4P state above the electron impact threshold. Projectile excitation is also produced by the target nucleus (electron‐nucleus Excitation [enE]) for the 2P± states. The eeE and enE cross sections were evaluated by Impulse Approximation (IA) and PWBA, respectively. The total KLL Auger electron production cross sections were also determined and exhibited the overall electron‐electron interaction effects of eeE and Resonant‐Transfer Excitation (RTE) which, in particular, is the 1s→2p excitation with 2p capture to result in 1s2s2p2 3,1D states.

Production of the O5+(1s2s2p 4PJ) states by electron excitation in 10–34 MeV collisions of O5+ ions with H2, He, Ne, Ar, Kr and Xe targets

Abstract Absolute double differential cross sections (DDCS) for electron production were determined for the Auger-decay of the (1s2s2sp 4P) state in 10–34 MeV collisions of O5+(1s22s) ions with H2, He, Ne, Ar, Kr, Xe targets using zero-degree projectile Auger-electron spectroscopy. Due to spin conservation, e-n interaction mechanisms are excluded to first order and thus the e-e interaction is expected to dominate the (1s 2 2s 2 S) a (1s2s2p 4 P) excitation. Auger electrons from the decay of the O5+(1s2s2p 4P) state to the O6+(1s2) ground state were observed. The electron scattering model, using calculated direct electron-ion impact excitation cross sections, was compared to the measured DDCS. These calculations included the effects of the alignment of the 4PJ ( J = 1 2 , 3 2 , 5 2 ) states and their subsequent angular-dependent Auger electron emission.

Zero-degree binary encounter electrons in fast collisions of highly charged F and O ions with H2 targets

Abstract Doubly differential cross sections (DDCS) for binary encounter electrons (BEe) produced by 0.5–2 MeV/u highly-charged F and O ions in collisions with H 2 gas targets have been studied at 0° with respect to the ion beam direction. The measured DDCS of the broad binary encounter peak was well described by a simple impulse approximation (IA) treatment for bare ions, and was demonstrated to provide in situ detection efficiency of the electron spectrometer. The projectile energy dependence of the BEe production for nonbare (clothed) projectiles is found to follow a scaled IA prediction, in which a BEe enhancement is consistently exhibited for the collision energy range studied.

Electron capture and excitation studied by state-resolved KLL Auger measurement in 0.25−2 MeV/u F7+(1s21S, 1s2s3S) + H2/He collisions

Abstract State-resolved KLL Auger cross sections were measured for collisions of 0.25−2 MeV/u F7+(1s21S, 1s2s3S) with H2 and He targets at 0°. The mechanisms for forming the 1s 2/2/ and 2 s 2 p 2S+1 L Auger states were identified to be single electron capture, 1s → 2p excitation, and nonresonant and resonant transfer excitation (RTE) by the 1s21S ground or 1s2s3S metastable states of the incoming projectile ions. The cross sections for the formation of the doubly excited states were extracted and compared with theory. In particular, the 1s2s2p4P state showed a projectile energy dependence of EP−n(n = 4.4 ± 0.3 for He and 5.4 ± 0.3 for H2 targets) in electron capture. The 1s2p22D state exhibited a strong RTE signature from the ground state. The 2s2p3P state produced by excitation of the metastable beam component showed a fair agreement with a PWBA calculation.

RTE with Li vapor target

Abstract High resolution projectile Auger electron spectroscopy is being used to measure cross sections for resonant transfer and excitation (RTE) as a function of projectile energy, in collisions of highly charged ions with a lithium vapor target. Previously H2 and He have been used [4] as targets for RTE studies via high resolution projectile Auger electron spectroscopy. With Li as a target we expect to see the effect of the loosely bound valence electron manifested as a narrow resonance peak sitting on the broader peak of the 1s electrons. By using Li-like F and O projectiles, direct comparison of resonance line shapes can be made with previously obtained RTE cross section [5], using a He target. Extension of the technique is being made to laser-excited Li-vapor target. Progress on this aspect of the experiment will be presented.