Browsing by Author "Schafer, David Allen"

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    Absolute differential cross sections for charge-transfer of keV-energy hydrogen ion and oxygen ion ions with atomic oxygen
    (1989) Schafer, David Allen; Stebbings, R. F.
    The major constituent in the atmosphere of the Earth at altitudes between 200 and 500km is atomic oxygen.$\sp1$ Collisions involving atomic oxygen are therefore important in this region of the atmosphere. Due to the difficulty in producing atomic oxygen in the laboratory, there are very few reported measurements of scattering cross sections with an atomic oxygen target.$\sp{2-6}$ We have undertaken an experimental program designed to measure absolute differential cross sections for various collision processes involving atomic oxygen. The oxygen atoms are produced through dissociation of O$\sb2$ in a microwave discharge, producing a target of atomic and molecular oxygen whose densities are inferred from measurements with an electron impact time of flight mass spectrometer.
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    Differential cross sections for neutral-neutral and charge-transfer collisions
    (1985) Schafer, David Allen; Stebbings, Ronald F.; Dunning, F. Barry; Mutchler, Gordon S.
    Absolute differential cross sections for neutral-neutral and charge—transfer collisions involving fast oxygen are presented. Neutral-neutral collisions are measured over the energy range 5-5eV, and between angles of .1 degrees and 5. degrees, while charge transfer measurements are presented for 15eV oxygen ions over the same angular range. A position sensitive detector is used to detect both the primary and scattered particles, yielding absolute differential cross sections. Target chambers with small ratios of length to exit aperture diameter are used and the end effects due to gas streaming out of the aperture are estimated by a Monte Carlo computer simulation. The excited state composition of the oxygen ion beam is considered, and differential cross sections for charge transfer are presented for both ground and excited-state oxygen ions.