F. Jousse et Ec. Delara, INDUCED INFRARED-ABSORPTION OF MOLECULAR-OXYGEN SORBED IN EXCHANGED A-ZEOLITES .1. INTENSITY ANALYSIS, Journal of physical chemistry, 100(1), 1996, pp. 233-237
This paper presents induced infrared spectra of oxygen sorbed in two c
alcium exchanged A zeolites. Changes of the vibrational band upon adso
rption include two effects: the appearance of an induced band, due to
the electric field of the zeolite, and a frequency shift of this band,
due to the interaction. An analysis of the evolution of the intensity
of the IR band with respect to the number of sorbed molecules is perf
ormed, yielding a value of the intensity of the electric field at the
adsorption site of O-2 in CaA. The value of 2.8 x 10(10) V/m derived f
rom this analysis is very high compared to the electric field observed
in other zeolites (0.8 x 10(10) V/m in NaA obtained with nitrogen or
1.1 x 10(10) V/m with methane). It probably reflects the large effecti
ve charge of the Ca cation in CaA and its position in an 8-ring window
of the cavity. This analysis also indicates that the oxygen molecule
coordinates end-on, in a linear or somewhat bent manner, to the Ca2+.