IR spectra of ¹²CO co-adsorbed with ¹³CO or H₂, and of H₂ co-adsorbed with different bases (CO, benzene, dimethyl ether, ammonia and trimethylamine) are studied on ZnO. Frequency shifts observed for the v(CO) and v(ZnH) vibrations are analysed taking into account that lateral interactions occur between coadsorbed molecules on the (101̄0) face. The discrete features observed in the case of ¹²CO-¹³CO and H₂-benzene mixtures are in agreement with a Monte Carlo modelling involving that repulsion prevents adsorption on two nearest sites. It explains, in particular, the occurrence of seven well-resolved maxima. With stronger bases like NH₃, only one perturbed v(ZnH) band is observed. The frequency shifts are explained involving the strength of the bases and their size.