  We present a theory for excitation of heavy hydrogen-like projectile-ions by
light target-atoms in collisions where the momentum transfers to the atom are
very large on the atomic scale. It is shown that in this process the electrons
and the nucleus of the atom behave as (quasi-) free particles with respect to
each other and that their motion is governed by the field of the nucleus of the
ion. The effect of this field on the atomic particles can be crucial for the
contribution to the excitation of the ion caused by the electrons of the atom.
Due to comparatively very large nuclear mass, however, this field can be
neglected in the calculation of the contribution to the excitation due to the
nucleus of the atom.
