The isotherms of molecular hydrogen isotopes adsorbed in NaA zeolite, measured by microgravimetry from 120 to 77 K, have been approached by the Dubinin model. The adsorbed amounts slightly increase from H2 to D2. This fact is related to the values of the covolumes of the species in the fluid phase. The heats of adsorption are around 10 kJ/mol and decrease with the adsorption amount. From the adsorption entropy we have estimated the external and librational frequencies.

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The infrared analysis of the induced bands of molecular hydrogen isotopes, adsorbed in NaA zeolite, shows several features; (i) when the amount of adsorbed molecules increases, the bands become complex, showing three components, which can be related to different energetic situation of the molecules in the cavity; (ii) the band frequency is lower than the gas frequency; for each species the shifts are proportional to the inverse square root of the mass (same interaction with the crystal); (iii) the absolute intensity increases when the temperature decreases, this is due to the fact that the molecule remains longer in the vicinity of the adsorption site where the electric field is the highest. Its amplitude is deduced from the absolute intensities measured at the lowest temperature (∼1010 V/m, in agreement with other results).