  A model of the asymmetric coherent scattering process (caused by initial
atomic wave-packet splitting in the momentum space) taking place at the large
detuning and adiabatic course of interaction for an effective two-state system
interacting with a standing wave of laser radiation is discussed. We show that
the same form of initial wave-packet splitting may lead to different, in
general, diffraction patterns for opposite, adiabatic and resonant, regimes of
the standing-wave scattering. We show that the scattering of the Gaussian wave
packet in the adiabatic case presents refraction (a limiting form of the
asymmetric scattering) in contrast to the bi-refringence (the limiting case of
the high-order narrowed scattering) occurring in the resonant scattering.
