Abstract : Study of isomeric states allows to gain important information on the structure of nuclei near as far from stability. This study also contributes to our understanding of the role of different reaction mechanisms in the population of high spin and high energy states in heavy-ion collisions at intermediate energies. The experiments have been successfully performed using an experimental setup placed at the LISE spectrometer at GANIL. In the first part of this thesis, an observation and study of isomeric states in neutron rich nuclei, near 78Ni, have been presented. During this experiment, ten new micro-second isomers have been observed and studied among the fragmentation reaction products induced by a 86Kr beam. The second part deals with the study of population of isomeric states, in peripheral reactions of a 92Mo beam at 60 MeV/u. Isomeric ratios F and momentum distributions of nuclei have been measured. A strong dependence of F on the structure of the isomer and on the reaction mechanism has been observed for the first time at intermediate energies.