Carbon and carbon nitride (CN) films were prepared under:ultrahigh vacuum condition;by ion beam deposition using isotopically mass-separated, energetic (50-400 eV) negative C-12(2)- and (CN-)-C-12-N-14 ions, respectively. The optical properties as well as structures and chemical composition of the films have been characterized and discussed as a function of the kinetic energy of C-2(-) and CN- ions, The structures of carbon and CN films in this study were hydrogen-free amorphous carbon (a-C) like. The N/C composition ratio of the CN films was N/C similar to 0.4,:although the arrival ratio of N/C was N/C = 1. The CN film properties depended weakly on kinetic energy of CN- ions, while on a-C films there were kinetic energy dependence of C-2(-) ions of optical constant observed.