Adsorption properties of copper ion-exchanged mordenite (CuM) for dinitrogen molecules (N-2) were examined at 298 K. The intensive IR absorption band observed at 2299 cm(-1) was attributed to the N-2 species strongly adsorbed on CuM. The interaction of N-2 With CuM is explored using adsorption calorimetry, X-ray absorption fine structure (XAFS), electron spin resonance (ESR), and photoemission spectroscopy. The differential heat and entropy of adsorption for N-2 on CuM were 60 kJ mol(-1) and 60 J K-1 mol(-1) at the initial stage of adsorption, respectively, and those for N-2 On NaM (sodium-type mordenite) gave the values of 32 kJ mol(-1) and 130 J K-1 mol(-1), revealing that the N-2 molecules are in the localized state resulting from the strong interaction with CuM. The monolayer capacity is estimated to be 4.12 cm(3) g(-1) for N-2 On CuM-150, which gives a value of 0.22 for the N-2/Cu ratio. XAFS and emission data for CuM degassed at 873 K exhibit pair bands at 8.983 and 8.994 keV and 18 700 and 20 800 cm(-1), respectively. The former pair band is assigned to the 1s-4p transition, and the latter pair band is assigned to the 3d(9)4s(1)-3d(10) transition. It is also found that the ESR band intensity for Cu(II) decreases with increasing pretreatment temperature. These spectral data are reasonably explained by assuming the presence of Cu(I) species in mordenite. It is proved from the emission data that the adsorption site including Cu(I) species easily formed by heat treatment at 873 K in vacuo is effective for N-2 adsorption. Such easy conversion of Cu(II) to Cu(I) may be due to the spatial distribution of ion-exchanged sites on mordenite. The appearance of a strong IR band at 2299 cm(-1) is due to the adsorption of N-2 On the Cu(I) species and to the induction of a transition moment by the strong field of this site. Although a rather high value of heat of adsorption might suggest chemisorption, it is made plausible that this type of N-2 adsorption is physisorption.