  A theoretical approach was developed to describe secondary particle emission
in heavy ion collisions, with special regards to pre-equilibrium
{\alpha}-particle production. Griffin's model of non-equilibrium processes is
used to account for the first stage of the compound system formation, while a
Monte Carlo statistical approach was used to describe the further decay from a
hot source at thermal equilibrium. The probabilities of neutron, proton and
{\alpha}-particle emission have been evaluated for both the equilibrium and
pre-equilibrium stages of the process. Fission and {\gamma}-ray emission
competition were also considered after equilibration. Effects due the possible
cluster structure of the projectile which has been excited during the
collisions have been experimentally evidenced studying the double differential
cross sections of p and {\alpha}-particles emitted in the E=250MeV 16O +116Sn
reaction. Calculations within the present model with different clusterization
probabilities have been compared to the experimental data.
