The ozone isotopic anomaly observed in early 1980s has been the first occurance of mass independent fractionation of chemical origin. Assigned first, essentially to the ozone formation process, recent works show additional contributions such as the photolysis process. This thesis uses a theoretical approach based on ab initio quantum chemistry and dynamics computations to obtain the absorption cross sections and their isotopic variations. The absorption cross sections allow to study ozone's photodissociation by solar irradiation (actinic flux) ; which enables an accurate evaluation of the photodissociation process in ozone's isotopic enrichment. Obtained results could be integrated in a global model that takes into account both ozone's formation and destruction processes.
