WATER-ADSORPTION ON ZEOLITES - AB-INITIO INTERPRETATION OF IR DATA

Ab-initio 6-31G* OH frequency calculations show the water molecule complex with the bridging OH group of zeolites to be hydrogen-bonded. The experimental 3390- and 3695-cm-1 frequencies of the complex are interpreted to belong to the water OH group interacting with the surface by two hydrogen bonds and to the other slightly perturbed water OH group, respectively. The broad approximately 2900-, approximately 2450-, and approximately 1700-cm-1 bands are explained on the basis of a theory of OH band profiles of hydrogen-bonded complexes to be the so-called (A, B, C) trio, caused by resonant interactions between the nu(OH) +/- nu(OH...O) combination modes and the delta(OH) and gamma(OH) overtones of the perturbed bridging OH group.