The shift and the change in intensity of the OH stretching bands of decationated near-faujasite (Y) zeolites have been studied with respect to the physical adsorption of N2, O2, CH4, Ar and Kr. The high-frequency OH stretching was assigned to hydroxyls in the supercage and the low-frequency OH stretching to hydroxyls in the cubo-octahedron. A simple electrostatic model allows one to correlate the shift and the change in intensity of the high-frequency OH band to the dielectric constant of adsorbed species. The reaction field of the OH dipole in an ellipsoidal cavity surrounded by the adsorbed molecules seems to be responsible for the perturbation undergone by the OH oscillator when the dielectric constant around the cavity is modified.