  We report the investigation of the influence of atomic motion on the
fluorescence dynamics of dilute atomic ensemble driven by resonant pulse
radiation. We show that even for sub-Doppler temperatures, the motion of atoms
can significantly affect the nature of both superradiation and subradiation. We
also demonstrate that, in the case of an ensemble of moving scatterers, it is
possible to observe the nonmonotonic time dependence of the fluorescence rate.
This leads to the fact that, in certain time intervals, increasing in
temperature causes not an decrease but increase of the fluorescence intensity
in the cone of coherent scattering. We have analyzed the role of the frequency
diffusion of secondary radiation as a result of multiple light scattering in an
optically dense medium. It is shown that spectrum broadening is the main factor
which determines radiation trapping upon resonant excitation. At later time,
after the trapping stage, the dynamics is dominated by close pairs of atoms
(dimers). The dynamics of the excited states of these dimers has been studied
in detail. It is shown that the change in the lifetime of the given adiabatic
term of the diatomic quasi-molecule induced by the change in the interatomic
distance as well as possible non-adiabatic transitions between sub- and
superradiant states caused by atomic motion can lead not to the anticipated
weakening of subradiation effect but to its enhancement.
