  The spin-dependent elastic reflection of quasi two-dimensional electrons from
a lateral impenetrable barrier in the presence of band-structure spin-orbit
coupling results in a spin angular impulse exerted on the electrons which is
proportional to the nontrivial difference between the electrons' momentum and
velocity. Even for an unpolarized incoming beam we find that the spin angular
impulse is nonzero when averaged over all components of the reflected beam. We
present a detailed analysis of the kinematics of this process.
