CLUSTER QUANTUM-CHEMICAL MINDO 3 STUDY OF THE NATURE OF HYDROXYL-GROUPS ON A CALCIUM-OXIDE SURFACE/

A modified MINDO/3 method was applied to study water molecule interact ion with a pure calcium oxide using a supermolecular approach. The cal cium oxide was modelled by a Ca32O32 four-layer molecular cluster cont aining all sets of the most chemically active low-coordinated calcium an oxygen ions (Ca-LC(2+) and O-LC(2-)). It is shown that the dissocia tive adsorption of water molecule on a pair of acid-base centers of Ca O is energetically more favorable than the molecular forms of adsorpti on on an acidic sites. O-H stretching frequencies of six kinds of hydr oxyl groups on a CaO calculated by a harmonic oscillator approach can be ascribed to the corresponding local structures.