Distinctive features of Coulomb-related emissions in peripheral heavy ion collisions at Fermi energies

Light charged particles emitted at about 90 deg in the frame of the projectile-like fragment in semi-peripheral collisions of 93Nb+93Nb at 38A MeV give evidence for the simultaneous occurrence of two different production mechanisms. This is demonstrated by differences in the kinetic energy spectra and in the isotopic composition of the particles. The emission with a softer kinetic energy spectrum and a low N/Z ratio for the hydrogen isotopes is attributed to an evaporation process. The harder emission, with a much higher N/Z ratio, can be attributed to a ``midvelocity'' process consisting of a non-isotropic emission, on a short time-scale, from the surface of the projectile-like fragment.