Adsorptions of O-2, H-2, and rare gases (He, Ar, Kr, and Xe) on H-mordenite at low temperatures were studied by transmission Fourier-transform infrared spectroscopy. Stretching bands of molecularly adsorbed O-2 and H-2 species were observed at 1549 and 4106 cm(-1), respectively. Isotope shifts observed for the O-18(2) and D-2 adsorption have confirmed these assignments. The introduction of the gases except He caused a downward shift and a broadening of the upsilon(OH) band of acidic OH groups at 3616 cm(-1). This perturbation is interpreted as a formation of a hydrogen-bonded complex between the acidic OH group and the adsorbate from a deconvolution analysis of the upsilon(OH) band. The perturbation by H-2 was qualitatively different from those by other gases. This is interpreted as an H-2 interaction both with the acidic OH group in a side-on type and with the framework oxygen next to the OH group, while other molecules interact solely with the bridging OH group in an end-on type.