A microscopic model based on the molecular dynamics concept was applie
d to study the early phase (t < 300 fm/c) of the Kr-84+Tb-159 reaction
at 45 MeV/nucleon. The calculations agree with the experimental obser
vation that the heavy ion reactions in the intermediate energy domain
are predominantly of binary nature, even for collisions associated wit
h a number of intermediate mass fragments. Collisions at small impact
parameters (b < 3 fm) lead to the formation of a hot composite system.