J.M. Sanders

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.

Impulse approximation treatment of electron-electron excitation and ionization in energetic ion-atom collisions

Abstract The effect of electron-electron interactions between projectile and target electrons observed in recent measurements of projectile K-shell excitation [T.J.M. Zouros et al., Phys. Rev. Lett. 62 (1989) 2261] and ionization [T.J.M. Zouros et al., Nucl. Instr. and Meth. B56/57 (1991) 107 and D.H. Lee et al., Phys. Rev. A46 (1992) 1374] using 0° projectile Auger electron spectroscopy are analysed within the framework of the impulse approximation (IA) [D. Brandt, Phys. Rev. A27 (1983) 1314]. The IA formulation is seen to give a good account of the threshold behavior of both ionization and excitation, while providing a remarkably simple intuitive picture of such electron-electron interactions in ion-atom collisions in general. Thus, the applicability of the IA treatment is extended to cover most known processes involving such interactions including resonance transfer excitation, binary encounter electron production, electron-electron excitation and ionization.

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.

One- and two-electron processes in collisions of heavy ions with H2 and He

Abstract In this paper we present a description of the apparatus and results for experiments involving one- and two-electron processes in collisions of heavy ions with H2 and He. The experiments were performed using one-electron and bare projectiles. In the first section we describe the measurement of pure ionization of one-electron projectiles by H2 targets and compare with previous results for He targets. We also present the results for one-electron capture by the projectiles from H2 targets. The energy dependence of the cross sections is compared to theoretical predictions for atomic and molecular hydrogen targets. Both experiments were performed by measuring only the final charge state of the projectile. In the second section we describe the measurement of partial cross sections for the same collisions by measuring the target recoil charge state in coincidence with the projectile charge state. By this method we can measure pure single- and double-ionization of the target, pure single-electron transfer and transfer ionization, and pure double-electron transfer. This experiment is presently being performed for bare fluorine on He; however, absolute cross sections are not available at the time of this conference.

Effect of electron-electron interaction on projectile K-shell ionization in energetic ion-atom collisions studied by 0° Auger electron spectroscopy

Abstract Cross sections for 1s ionization of the ground state of O 4 (1s 2 2s 2 ) were obtained in 10–30 MeV collisions of O 4+ with H 2 and He targets. High resolution Auger electron spectroscopy was used to detect at 0° with respect to the beam direction, the electrons emitted from the Auger decay of O 5+ (1s2s 2 ) → O 6+ (1s 2 ) + e − following 1s ionization of the O 4+ ions. The electron-nucleus ( σ enI ) and electron-electron ( σ eeI ) ionization cross sections, due to ionization of the projectile electron either by the target nucleus or the target electrons, respectively, were independently computed. σ enI was calculated within a PWBA treatment, while σ eeI was computed within an impulse approximation (IA) treatment of electron impact ionization of O 4+ . The incoherent sum σ enI + σ eei was found to be in good agreement with the data. K-shell ionization of the metastable O 4+ (1s 2 2s2p 3 P) component of the beam was also observed.

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.

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.

Interference between RTEA and elastically scattered target electrons in 20 MeV F6+ + H2 collisions

High‐resolution high‐statistics Auger electron spectra were obtained in collisions of 20 MeV F6+ (1s22s) projectiles with H2 targets using 0° projectile electron spectroscopy. The 1s2s2p2 3,1D→1s22s (D—transitions) and the 1s2s2p2 1D→1s22p (D—transition) Auger transitions were clearly resolved. The 1s2s2p2 3,1D projectile states can be formed by Resonance Transfer and Excitation (RTE),1,2 and thus their Auger decay to the 1s22s state can interfere with elastically scattered target electrons giving rise to characteristic Fano‐like line shapes. Their Auger decay to the 1s22p state can interfere with inelastically scattered target electrons. Comparison with the results of existing RTEA‐elastic electron scattering interference theory and asymmetry parameter are discussed. For the RTEA‐inelastic electron scattering interference, calculations will soon be available.

Energy shifts in the binary encounter peak of 0.5 MeV/amu Cuq+ +H2

The energy shifts from the classical prediction in the binary encounter peak of Cuq+ as a function of the charge state q has been experimentally measured. The data showed that this shift increases by increasing the charge state of the projectile. We fitted the energy shift to an equation of the form ΔE=aqn and obtained a value for the exponent n. The data is also compared to the Bohr‐Lindhard calculation which predicts an exponent n=0.5. Good agreement was found between our data and the Bohr‐Lindhard model.