L.N. Tunnell

Angular distributions of reaction products from low energy capture by multicharged ions

Abstract The angular deflection of the projectile which occurs when a slow multiply charged ion captures electrons from a neutral target depends sensitively on the potential curve history of the interaction throughout the encounter. We have measured angular distributions for a variety of projectiles capturing from targets of He, Ar and d2. Some of the major features may be understood in terms of classical deflection functions for the heavy particle motion. Where quantal treatments of the scattering is available, the calculations are in good agreement with the data.

Angular distributions of slow multiply charged ions following capture

Abstract When slow, multiply charged projectiles capture electrons from neutral targets, the angular distributions of the capturing particles are much more sensitive to the potential curves involved than are the total cross sections. We have constructed an apparatus suitable for measuring angular distributions of these capture products. A position sensitive channel plate chevron followed by a resistive anode is used to determine the scattering angle and a simple retarding grid system is used to select the final charge states. Multiply charged projectiles are obtained from recoil ion sources pumped by fast ion beams from the KSU tandem accelerator. Systems studied include Neq+, Cq+ and Arq+, with q lying between 3 and 8, on targets of He, D2 and Ar at accelerating v and 350 V. Selected cases will be presented and discussed.

On the dynamical description of K-K charge transfer in highly ionised ion-atom collision systems

Examines the role of electronic relaxation in the description of K-K charge transfer for ion-atom collisions with bare or one-electron projectiles in the intermediate velocity region. Total differential K-K transfer cross sections for the system F9+Si are calculated within the coupled-state impact parameter method, starting from a relaxed molecular Hamiltonian and from a frozen two-centre Hamiltonian. By comparing the results of the two molecular expansion calculations with each other and with those of the atomic orbital expansion method. The authors test the various assumptions about relaxation of passive as well as active electron orbitals in a single-electron molecular orbital picture. A comparison with experimental data favours the description with relaxation in neither active nor passive orbitals for collision energies above 400 keV amu-1.

Subshell electron capture cross sections of argon atoms by protons

Discusses a non-perturbative ab initio theory for evaluating electron transfer cross sections from the individual subshells of multi-electron atoms by heavy projectile in the keV/amu to the MeV/amu energy region. By employing a two-state two-centre atomic eigenfunction expansion and an independent-electron approximation with a realistic Herman-Skillman potential for the target atom, the charge transfer cross sections from the individual subshells of argon atoms by protons have been calculated.

An experimental apparatus for translational energy spectroscopy for low energy Xq+ on atomic hydrogen

Abstract The design and performance of a system for performing translational energy spectroscopy on atomic hydrogen targets is presented. Low energy highly-charged ions are produced in a recoil ion source through collisions between target gases and a heavy, fast pump beam from the EN tandem accelerator. These ions are directed through a double-focusing magnetic spectrometer which selects the desired projectile charge state. An atomic hydrogen target is produced in a thermal dissociation oven. The energy and final charge states of the product ions are determined by a double-focusing, hemispherical electrostatic analyzer. The current work concentrates on the change in energy of the projectile ions accompanying electron capture for 250 eV per charge argon projectiles.