QUANTUM CHEMICAL MOLECULAR-MODELS OF OXIDES .1. REPRODUCTION OF STRETCHING VIBRATIONAL FREQUENCIES OF SURFACE OH GROUPS

Quantum chemical molecular models reproduce the O-H stretching vibrational frequencies of -> Si-OH, -> P-OH, > B-OH, and -> Al-OH surface groups of oxides within 11 cm-1 of the experimental data. The calculations are carried out by the ab initio SCF-MO method with the 3-21G basis set, using the scaling procedure for O-H bond force constants correction. Application of this approach allows prediction of a structure of the strongly acid OH groups in amorphous aluminosilicates and hydrothermally treated zeolites, which manifest themselves in the band in the range 3720-3740 cm-1. This structure is also confirmed by the calculations of the O-H vibrational frequency shifts under the influence of acetonitrile adsorption.