Interaction between probe molecules and zeolites. Part II: Interpretation of the IR spectra of CO and N-2 adsorbed in NaY and NaRbY

The interaction energy and band shift values of the fundamental vibrational modes of CO and N-2 adsorbed within the NaY and NaRbY zeolite forms are calculated using a pair-wise addition scheme. A clear difference between the most stable positions of CO and N-2 in NaY and NaRbY is observed. While, for NaY, both diatomic probes are close to the alkali-metal ion, this is not the case for NaRbY. For CO, the isolated Rb+-CO pair-wise interaction cannot describe the system, because the Rb-CO and O-CO distances are comparable whereas for N-2 within NaRbY, the molecule is closer to the framework oxygens than to the Rb. The influence of both molecular and zeolite framework parameters (ionic charges, polarizabilities, and radius) on the interaction energy and band shift values is definitively proven.