Collect. Czech. Chem. Commun. 1988, 53, 2191-2202

Vibrational properties of surface hydroxyls: Nonempirical model calculations including anharmonicities

Hartmut Mixa, Joachim Sauerb, Klaus-Peter Schröderb and Angela Merkelb

a Sektion Physik der Karl-Marx-Universität Leipzig, Leipzig, 7010, DDR
b Zentralinstitut für physikalische Chemie der Akademie der Wissenschaften der DDR, Berlin-Adlershof, 1199, DDR


Complete sets of harmonic, semidiagonal cubic as well as diagonal cubic and quartic force constants are reported for the internal coordinates of terminal, ≣SiOH, and bridging, ≣SiOH·Al≣, surface hydroxyls on silica and zeolites. They are obtained by numerical differentiation of analytically calculated gradients of the energy (SCF approximation, 6-31 G* basis set). A GF vibrational analysis is performed and after making a nonlinear transformation of the force constants into normal coordinates the anharmonicity constants are evaluated by perturbation theory. Comparison is made with the D2OH+ ion and the DOH molecule. The calculated anharmonicities of the OH bonds in the systems studied are remarkably constant and vary between -76 and -84 cm-1, only in agreement with the values observed for DOH (-83 cm-1) and surface silanols, ≣SiOH (-90 ± 15 cm-1).