Infrared spectroscopic studies have shown that adsorbed carbon monoxide interacts with Bronsted acid Si(OH)A1 groups of the zeolite H-ZSM-5 forming hydrogen bonded H⋯CO and H⋯OC species, which were characterized by C-O stretching IR absorption bands at 2174 and 2120 cm^-1, respectively. In the rubidium-exchanged zeolite, corresponding Rb⁺⋯CO and Rb⁺⋯OC adducts gave characteristic bands at 2161 and 2119 cm^-1, respectively. Variable-temperature FTIR spectroscopy has shown that, in both cases, C- and O-bonded species are interrelated through a temperature dependent equilibrium in which the proportion of Obonded adducts increases with increasing temperature. By means of van't Hoff plots, the corresponding enthalpy change was found to be ΔH°= 4.6 kJ mol^-1 for the CO/H-ZSM-5 system and ΔH°= 1.8 kJ mol^-1 for CO/Rb-ZSM-5.