Orientation and alignment parameters in e+- impact excitation of hydrogen-like positive ions

The orientation () and alignment angle (γ) of the excited 2p state of hydrogen-like positive ions by high-energy electron and positron impact are calculated in the Coulomb-Born approximation. We also analyse the shape and rotation of the excited state in terms of the dipole and velocity and γ on the projectile velocity and target nuclear charge Z is also investigated. Our results reveal that the classical grazing model, which interprets positive (negative) in terms of an attractive (repulsive) force between the projectile and the target, is not valid in general. We also report the orientation and alignment angle for the 3d state of He+ excited by electron and positron impact. (author)