Interaction of diatomic (polar) molecules with the surface of ionic solids is analysed by means of an electrostatic model which takes into account ion-dipole and ion-quadrupole interactions. This model was found to be capable of predicting the geometry of the adsorption complex, formation of isomeric states and relevant features of characteristic vibrational spectra. The theoretical model is demonstrated by considering the case of CO adsorbed on cation-exchanged zeolites for which a wealth of experimental data is available from both, vibrational spectroscopy and adsorption calorimetry. However, extension to other systems should be fairly straightforward.