CdS thin films with different compositions were deposited by the electrospray pyrolysis of CdCl2 and (NH2)2 CS solutions mixed in different proportions. The diverse morphology of the films was analyzed using AFM/SEM observations. The relative atomic concentrations of Cd and S species in the bulk, and at the surface of the films were estimated using EDS and XPS quantification routines, respectively. It was found that the surfaces of all types of investigated films were enriched by metallic species and the atomic surface ratio of Cd/S was between 1.6 and 3.2. Chemisorption of oxygen and carbon monoxide on the film surfaces at low temperatures between 290 K and 500 K has been studied in order to get information about Cd surface sites on the chemisorption. Metallic surface species are considered as basic centres for the chemisorption of CO and O2 gases. Three different oxygen species with different binding energies for Ols electrons were found on the film surfaces. The electronic structure of the surface complex CO, together with its influence on the charge transfer reactions during excitation are discussed in terms of a model based on the correlation between collective electronic characteristics of the crystal and local quantum-mechanical parameters of the chemisorbed complex.