Apolar ices have been observed in several regions in dense clouds and are likely dominated by molecules such as CO, CO(2) and the infrared inactive molecules O(2) and N(2). Interstellar solid CO has been well characterized by ground-based high resolution measurements. Recent ISO results showed the ubiquitous presence of abundant CO(2) ice and the presence of CO(2)-rich ice mantles towards several molecular clouds. CO and CO(2) have sharp bands in the infrared and their band shape depends strongly on the ice composition. The profiles of the strong CO and CO(2) bands can therefore provide important information on the composition, temperature and thermal history of interstellar and precometary ices.We address, in this paper, the infrared spectra of 70 apolar ice mixtures of pure, binary, and multicomponent type. We studied their spectral properties at 10 K, during warm up and UV photolysis, and derived the optical constants. We discuss the importance of particle shape calculations for strong transitions such as CO and CO(2).In the laboratory context, we investigate the formation of CO(2) in the interstellar medium by UV photolysis of interstellar ices. Together with astronomical spectra taken by the ISO satellite these laboratory data will be extremely valuable for the determination of the grain mantle composition in dense clouds.