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We have measured the double differential cross sections (DDCS) ({ital d}{sup 2}{sigma}/{ital d}{var_epsilon}{sub {ital ed}}{Omega}{sub {ital e}}) of low-energy electron emission in the ionization of H{sub 2} bombarded by bare carbon ions of energy 30 MeV. The energy and angular distributions of the electron DDCS have been obtained for 12 different emission angles and for electron energies varying between 0.1 and 300 eV. We have also deduced the single differential and total ionization cross section from the measured DDCS. The data have been compared with the predictions of first Born approximations and the CDW-EIS (continuum distorted wave{endash}eikonal initial state) model. The CDW-EIS model provides an excellent agreement with the data. {copyright} {ital 1996 The American Physical Society.}

Absolute ionization cross sections for 28{endash}114-keV helium ion impact on atomic hydrogen, differential in energy and angle of the ejected electrons, have been obtained from crossed-beam measurements and previously measured cross sections for molecular hydrogen targets. A radio frequency discharge source produced a mixed atomic and molecular target with a typical dissociation fraction of 74{percent}. Energy spectra were measured from 1.5 to 130 eV by an electrostatic analyzer with a resolution of 5{percent}. The angular range was 15{degree}{endash}160{degree}. Results are compared with calculations based on the first Born, continuum-distorted-wave{endash}eikonal-initial-state, and classical trajectory Monte Carlo methods. Total electron yields are obtained by combining calculations that are separately performed for liberating the target and projectile electrons. Model potentials are used to represent the interparticle-separation-dependent screening of the nuclear charges experienced by the electrons. Though projectile electron emission is a negligible component of the total ionization cross section for the present collision energies, its contribution is significant for particular regions of the spectrum of ejected electrons. Through comparison with our proton-impact data [Kerby {ital et} {ital al}., Phys. Rev. A {bold 51}, 2256 (1995)], differences and similarities are demonstrated owing to the common asymptotic charge of these two projectiles but differing nuclear charges more » and the electron carried by the He{sup +} ion. Comparisons are also made illustrating the differences between atomic and molecular hydrogen targets. {copyright} {ital 1996 The American Physical Society.} « less

The fundamental process of ionization in the collisions of protons with atomic hydrogen is considered at an impact energy of 70 keV by comparing experimental and theoretical doubly differential cross sections for electron ejection. This collision system provides a critical test of intermediate energy theories since effects such as electron-electron interaction (correlation) are not present and the roles of the ionization mechanism and subsequent evolution of the ejected electron in the two-centre Coulomb field are isolated. Results of the classical-trajectory Monte Carlo technique, the continuum distorted wave-eikonal initial state method and the plane wave Born approximation are compared with the present experimental data which are the first differential measurements that have been performed for the ionization of atomic hydrogen by proton impact.