  It is shown that the population Rabi-floppings in a lossless two-level atom,
interacting with a monochromatic electromagnetic field, in general are
convergent in time. The well-known continuous floppings take place because the
restricted choosing of initial conditions, that is when the atom initially is
chosen on ground or excited level before the interaction, simultaneously having
a definite value of momentum there. The convergence of Rabi-floppings in atomic
wave-packet-states is a direct consequence of Doppler effect on optical
transition rates (Rabi-frequencies): it gradually leads to ''irregular''
chaotic-type distributions of momentum in ground and excited energy levels,
smearing the amplitudes of Rabi-floppings. Conjointly with Rabi-floppings, the
coherent accumulation of momentum on each internal energy level monotonically
diminishes too.
