H. Aliabadi

Ionization and excitation of hydrogen molecules by fast proton impact

The ratio of ionization - excitation to single ionization of hydrogen molecules caused by fast proton impact was measured over a wide velocity range (v = 6 - 24 au) using the coincidence time-of-flight technique. This ratio, %, is independent of the collision velocity at high velocities. It differs from the ratio of total to production mostly due to a large contribution from the dissociation of the electronic ground state of the molecular ion. The dissociation fraction of was measured and compares well with our calculations using the Franck - Condon approximation.

One and two electron processes in fast collisions between protons and hydrogen molecules

Abstract The ratio of double to single ionization of hydrogen molecules caused by fast proton impact was measured over a wide velocity range (v = 6–24 a.u.) using the coincidence time-of-flight technique. This ratio, ∼ 0.13% at high velocities, is about a factor of 2 smaller than the same ratio for the He target. This difference is due mainly to the larger single ionization cross section for hydrogen molecules, i.e. σ+(H2) ∼ 2 σ+(He). The double ionization cross section, on the other hand, is similar for both He and H2. Furthermore, the ratio of double to single ionization of the hydrogen molecule by proton impact is smaller than the one caused by electron impact at the same velocity in a similar way as for the helium target.

Transfer Ionization to single capture ratio for fast multiply charged ions on He

The charge state and energy dependences of Transfer Ionization (TI) and Single Capture (SC) processes are being investigated. The collision systems reported here are O(4–8)+ ions interacting with Helium. The measurement is being made for beam energy 1 MeV/u using a supersonic He jet with two-stage collimation. A recoil ion momentum spectrometer is used to separate TI and SC by recording the longitudinal momentum transfer and time-of-flight of the recoil ions. A magnetic field is used to control the position of the recoil ions on the detector. The ratios of TI to SC are determined with high accuracy and are compared with previous results. Higher Z-ions are under investigation.

Zero-degree auger electron spectroscopy of quasi-free electrons scattered by highly charged ions

Ion-atom collisions can be used to determine singly differential electron scattering cross-sections for the direct and resonant, elastic and inelastic electron-ion collisions. A new high-resolution tandem parallel-plate electron spectrometer system capable of sub eV resolution has been designed and constructed. This spectrometer has been used to analyze electrons up to 12 keV in energy. An estimated analysis limit of 21 keV has been determined, which will allow the measurement of the 2p2 resonances up to Z=22. We will report the results of direct and resonant elastic scattering studies for hydrogen-like F, Mg, and Si ions.

An experimental method for evaluating the H2 and D2 contamination levels in a HD bottle

Abstract Studies of one- and two-electron processes in collisions with hydrogen molecules using the time-of-flight technique are simplified by using the heteronuclear HD isotope because the H+ and D+ fragments can be easily distinguished from each other. The difference in the time-of-flight of H+ and D+ enable the fragments to be measured in coincidence with each other. However, it is hard to determine the purity of the HD target, in particular the H2 contamination, because the H2+ molecular ions coincide with the D+ fragments. A method is suggested to determine the purity of a HD target to a precision of a few percent. This method is based on measuring the yield of very slow ( 1 MeV). The H2 contamination is then determined by subtracting the theoretically evaluated contribution of the ground-state dissociation of the HD+ molecular ion from the measured sum of both H+ and D+ low-energy fragments.