ROLE OF PROJECTILE CONTINUUM STATES IN THE IONIZATION OF ATOMIC-HYDROGEN BY HIGH-ENERGY ION IMPACT

Ionization of atomic hydrogen in collisions with H+ and He2+ ions is studied by a large-scale coupled-channel calculation. It is demonstrated that high-lying continuum states of the projectile, which have been disregarded in previous calculations, contribute significantly to the ionization of the target atom. The portion of the ionization into these projectile continuum states amounts to 13% of the total ionization cross section in the case of H+ impact even in the MeV region, and the question is raised as to the normalization procedure of experimental values to the Born cross section there. The partial cross section of the ionization into the target continuum satisfies the Z2 scaling rule (where Z is the projectile charge) at high energies while the component into the projectile continuum states has a weaker dependence on the charge. As a result the ratio of the total ionization cross sections by He2+ and H+ impact deviates from the Z2 scaling by 4-5% above the collision energy of 500 keV u-1 in close agreement with the experimental findings of Shah and Gilbody.