2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/191236In this paper we discuss the reaction mechanisms that occur in the overlap zone for semi-peripheral heavy ion collisions at intermediate energies. In particular we focus on the development of neck instabilities, that could determine a possible increase of dynamical fluctuations. As observed in recent experimental data, at beam energies just above 10 MeV/A the most relevant expected consequence is the possibility to obtain large variances in the projectile-like and target-like observables. With increasing beam energy we pass to a mid-rapidity fragment production. In this way we predict a smooth transition from a deep-inelastic to a fragmentation reaction mechanism.14 pages, REVTEX, 2 ps figures, submitted to Phys.Rev.CNuclear Theorytext