A method for computer modelling of the IR spectra of disordered layers of molecules adsorbed on crystal surface is developed. The method includes MC simulation of surface diffusion induced by intermolecular interaction, calculating the frequency of each molecule in the local electric field of the surrounding molecules, and, finally, computing the spectrum of the layer of molecules, interacting by the mechanism of dynamic dipole coupling. Application for CO adsorbed on (1010) face of ZnO has shown that the computed spectra reproduce well most of the features observed in the experiment. The role of vibrational polarizability and bandwidth of individual molecules as well as of the structure of the layer and frequency distribution of molecules in the formation of dynamic spectra was analysed in model calculations with arbitrary chosen surface geometry and parameters. Dynamic interaction is shown to account for the band narrowing or intensity anomalies near saturating conditions and for the elimination of the structure caused by static interaction or surface inhomogeneity. It could either affect the band contour or even produce the fine structure in the spectra of isotopic mixtures adsorbed on homogeneous surfaces.