Determination of the electric field in zeolites NaA, NaCaA and Ca6A. Calculation from the ionic charge distribution and infrared measurements of the induced band of N2

Abstract

The fields in the cavities of NaA, CaNaA and Ca₆A zeolites have been determined by calculations from the ionic charge distribution and by experimental measurements of the infrared induced band of adsorbed N₂. We present a comparison between the calculated values obtained by considering two models of the charge distribution. This shows that the approximation in which the negative charge of the anionic framework is distributed on the oxygens only is valuable. The area of the induced band is proportional to the number of molecules per cavity, determined from isotherms, and to the absolute intensity, A, which in turn is proportional to the square of the field. This intensity reflects the mobility of the adsorbed molecule: measurements made at different temperatures show that the molecule should be localized at ca. 193 K. We find that the field is higher in CA₆A (0.78 V Å^–1) than in CaNaA (0.69 V Å^–1) and in NaA (0.51 V Å^–1).