POTENTIAL ENERGIES AND IR-SPECTRA FOR HOMOPOLAR DIATOMIC ADSORBATES OVER ION-EXCHANGED ZSM-5 ZEOLITES

Potential energies for N2, D2, and O2 entrapped in pores of MeZSM-5 (Me = Li, Na, K, Rb, and Cs) zeolites have been investigated theoretically as a basis for understanding the characteristic IR spectra of the adsorption systems. The adsorption potential proposed gives a reasonable value for the initial heat of adsorption q(st)0 and enables us to predict the mode of orientation of an admolecule at the cation site. Specific predictions include an end-on orientation for N2, a lying-down orientation for D2, and a random orientation for O2. Analysis of the IR spectral intensity of the adsorbed molecule proves also that the predicted molecular orientation is realistic. Furthermore, the IR peak shifts predicted theoretically by using the adsorption potential are in good agreement with the experimental results. The influence of the orientation of the admolecule upon the IR peak shift is thus clarified.