IR STUDY OF INTERACTIONS BETWEEN DIFFERENT MOLECULES COADSORBED ON ZNO

IR spectra of (CO)C-12 co-adsorbed with (CO)-C-13 or H-2, and of H-2 co-adsorbed with different bases (CO, benzene, dimethyl ether, ammonia and trimethylamine) are studied on ZnO. Frequency shifts observed for the nu(CO) and nu(Zn-H) vibrations are analysed taking into account that lateral interactions occur between coadsorbed molecules on the (1010BAR) face. The discrete features observed in the case (CO)-C-12-(CO)-C-13 and H-2-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 nu(Zn-H) band is observed. The frequency shifts are explained involving the strength of the bases and their size.