Anisotropies in the distribution of electrons captured to continuum states of a fast moving charge

The second-order Born approximation is considered for a charge transfer process to study electron capture to continuum states of a fast bare charge after a collision with a hydrogenic atom. By relaxing usual approximations, it is possible to take full account of the corrections to the upsilon-12 asymptotic behaviour of the cross section with impact velocity upsilon, and consequently to obtain the angular dependence of the electron distribution around the projectile. There is a dominating upsilon-14 ln upsilon anisotropic term, which is due to a contribution to the transition amplitude coming from the neighbourhood of the pole in the free-particles Green's propagator. The large value of the corrections to the upsilon-12 dependence of the cross section casts doubts on the validity of such asymptotic expansions for non-relativistic velocities. (author)