The adsorption of CH(D)Cl₃ and CHF₃ on a series of alkali-exchanged Y-zeolites was studied by ¹H- and ²³Na-NMR and by FTIR spectroscopy. Several adsorption structures were detected which involve H-bonding C–H(D)···O_Z between the acidic C–H(D) group and basic O_Z-framework atoms and between the exchangeable cations and halogen atoms of the probe molecules. ¹H-NMR demonstrated rapid exchange between several adsorption species and IR spectroscopy permitted detection of at least two different species, namely purely H-bonded species I and species II and/or III involving cation–halogen interactions. It is inferred that these species can undergo facile interconversion and that such processes may be involved in the rapid exchange as detected by NMR. Based on ²³Na-NMR results it is concluded that adsorption of CHCl₃ on NaY modifies the negative charge distribution in the zeolite framework. The adsorption-induced C–H(D)-stretching frequency shift of trichloromethane is considered to be a measure of the base strength of the framework O_Z-atoms.