Six distinct C-O stretch vibrational bands of varying intensity and with maxima at 2120, 2136, 2150, 2170, 2182, and 2195 cm(-1) were observed during the room-temperature adsorption of CO over NaY zeolite. This was accompanied by the appearance of a prominent band at 2356 cm(-1) along with the sidebands at 2336, 2342-2348, and 2364-2370 cm(-1) in the nu(3) region of CO2 vibrations. The intensity and the frequency of these bands showed monotonic changes on evacuation, temperature rise, and exchange of Na+ ions with a proton or a group IIA cation and also on using the isotopically labeled CO. For instance, the adsorption of isotopic (CO)-C-13-O-16 and (CO)-C-12-O-18 gases gave rise to a uniform red shift in all the major nu(CO) bands, corresponding to a frequency ratio of nu((CO)-C-13)/nu((CO)-C-12) approximate to 0.978 and nu((CO)-O-18)/nu((CO)-O-16) approximate to 0.976. Similarly, all the asymmetric stretching bands of CO2 showed a uniform isotopic shift corresponding to nu(C-13)/nu(C-12) approximate to 0.971. Furthermore, the intensity of most of the above-mentioned bands in nu(CO) and nu(3)(CO2) regions exhibited an exponential type growth behavior with increasing adsorbate pressure, though the extent of this growth was different for individual vibrations. No significant change was, however, observed in the frequency and the intensity of the hydroxyl region bands on adsorption of CO under experimental conditions of this study. Arguments are presented to show that the observations of this study are not in harmony with the reported modes of direct CO adsorption at the specific zeolitic sites such as the charge-balancing cations, Al3+ sites, or the Bronsted acid sites. Instead, the formation of the weakly held (CO)(n) and (CO2)(n) molecular clusters occluded in the zeolitic cavities and stabilized under the cation field is in conformity with the data of this study.