Invariant transverse-velocity spectra of intermediate-mass fragments were measured with the $4\pi$ multidetector system INDRA for collisions of ${}^{197}\mathrm{Au}$ on ${}^{197}\mathrm{Au}$ at incident energies between 40 and 150 MeV per nucleon. Their scaling properties as a function of incident energy and atomic number Z are used to distinguish and characterize the emissions in (i) peripheral collisions at the projectile and target rapidities, and in (ii) central and (iii) peripheral collisions near midrapidity. The importance of dynamical effects is evident in all three cases and their origin is discussed.

• Received 22 April 2002

DOI:https://doi.org/10.1103/PhysRevC.66.064606