FT-IR spectroscopy and theoretical ab initio as well as density functional (DFT) methods have been applied to the investigation of the interaction of N2O with Ag+ counter-cations in a ZSM-5 zeolite. As a preliminary part of the study, the adsorption of N2O on the parent H-Na-ZSM-5 zeolite (from which the Ag-ZSM-5 system was obtained by ion exchange) and the adsorption of CO at low temperature on Ag-ZSM-5, in order to monitor the dispersion of the Ag+ ions, were also performed. It was observed that N2O could be adsorbed on Ag+ counter-cations both N-end and O-end down. The two forms produce distinct bands due to the nu(NN) mode, clearly observable in the 2300-2200 cm(-1) range. Conversely, only the nu(NO) band due to the N-end down adduct was observed at 1325 cm(-1), the component corresponding to the O-end down form falling below the low frequency limit of IR transparency of the system. Interestingly, the band due to the nu(NN) mode of N2O molecules O-end down adsorbed on Ag+ ions appeared coincident with that of N2O in interaction with Al-OH and dropSi-OH-Aldrop groups left in the zeolite after exchange with Ag+. However, the former N2O adducts on silver cations appeared to be slightly more stable (less reversible) than the latter adducts. (C) 2003 Elsevier Science B.V. All rights reserved.