IMPROVEMENTS IN AB-INITIO CALCULATED OH STRETCHING FREQUENCIES OF ZEOLITE ACID SITE MODELS AND OTHER OH-CONTAINING MOLECULES, USING A MORSEPOTENTIAL

Ab initio calculations have been performed on a series of OH-containin g molecules, at the HF/6-311G* and MP2/6-311G** levels of theory. The molecules include H3SiOHAlH3 and H3SiOH, used as models of a Bronsted acid site and terminal silica hydroxyls in zeolites. A Morse potentia l is used to determine the OH stretching frequency of these molecules. The results show substantial improvement in the quality of the predic ted frequencies compared to experimental data, at both levels of theor y. In the case of closest agreement, the Morse MP2 OH stretching frequ encies of ClOH and H3SiOH are predicted to within 2% of the experiment al values.