  The particle emission at intermediate velocities in mass asymmetric reactions
is studied within the framework of classical molecular dynamics. Two reactions
in the Fermi energy domain were modelized, $^{58}$Ni+C and $^{58}$Ni+Au at 34.5
MeV/nucleon. The availability of microscopic correlations at all times allowed
a detailed study of the fragment formation process. Special attention was paid
to the physical origin of fragments and emission timescales, which allowed us
to disentangle the different processes involved in the mid-rapidity particle
production. Consequently, a clear distinction between a prompt pre- equilibrium
emission and a delayed aligned asymmetric breakup of the heavier partner of the
reaction was achieved.
