METHOD FOR THE CALCULATION OF THE VIBRATIONAL FREQUENCY-SHIFT OF PHYSISORBED MOLECULES - APPLICATION TO H-2 ADSORBED IN NAA ZEOLITE

The vibrational frequency shift of physisorbed diatomic molecules is r elated to the interaction with the adsorbent expressed in terms of the internuclear distance rho. It is calculated by the Schrodinger equati on, the perturbation theory, and a simplified method. We show that it is sufficient to calculate the interaction potential for the values of rho in the ground and first vibrational states in order to get a prec ision of 10% on the frequency shift. The comparison between the theore tical and experimental frequency shift of H-2 adsorbed in NaA zeolite is used to adjust the interaction potential, especially in terms of th e ionicity of the crystal.