Intermediate mass fragments fromAr40+197Au: Transition from the incomplete fusion to the participant spectator regime

Inclusive cross sections of intermediate mass fragments from the reaction ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$ ${+}^{197}$Au at E/A=30 and 220 MeV were measured with a low threshold and over a large range of angles. The integrated cross sections are about 2 b at both energies but the emission characteristics change considerably. The increased isotropy of the angular distributions and the strongly reduced Coulomb repulsion at the higher bombarding energy suggest that the emission process evolves towards fragmentation of excited spectator matter in central ion-ion collisions.