3-DIMENSIONAL RECOIL-ION MOMENTUM ANALYSES IN 8.7 MEV O7-HE COLLISIONS()

Using high-resolution recoil-ion momentum spectroscopy we have measure d the differential cross sections of single-electron capture and targe t single-ionization processes for 8.7 MeV O7+-He collisions as functio ns of scattering angle. A transverse momentum resolution of +/-0.2 au, which corresponds to an angular resolution of about +/-1.5x10(-6) rad for the projectile scattering angle, was obtained by intersecting a w ell collimated O7+ beam with a target of a supersonic He jet from a pr e-cooled gas and by measuring the recoil-ion transverse momentum. For the single capture reaction, information on the n-value of the electro n final state in O6+(1snl) is obtained from the longitudinal momentum of the recoil ions. In pure single-electron capture, the dominant cont ributions to capture were found to be those from the n = 4 and higher states, whereas single capture accompanied by the ionization of the se cond target electron mainly populates n = 2 to n = 4 states. Furthermo re, the measured transverse momentum distribution differs significantl y between pure single capture and capture with simultaneous ionization . The measured data for the pure capture process compare favourably wi th theoretical results based on a molecular-state expansion method. Ot her experimental data are discussed in terms of the classical overbarr ier model.